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Birth by vacuum extraction delivery and school performance at 16 years of age Mia Ahlberg, RNM; Cecilia Eke´us, PhD; Anders Hjern, PhD OBJECTIVE: The aim of the present study was to investigate cognitive competence, as indicated by school performance, at 16 years of age, in children delivered by vacuum extraction. STUDY DESIGN: This was a register study of a national cohort of 126,032 16 year olds born as singletons, with a vertex presentation, at a gestational age of 34 weeks or older, with Swedish-born parents, delivered between 1990 and 1993 without major congenital malformations. Linear regression was used to analyze mode of delivery in relation to mean scores from national tests in mathematics (40.2; scale, 10-75; SD, 14.9) and mean average grades (223.8; scale, 10-320; SD, 52.3), with adjustment for perinatal and sociodemographic confounders. RESULTS: Children delivered by vacuum extraction (e0.51; 95% confidence interval [CI], e0.76 to 0.26) as well as by nonplanned cesarean section (e0.51; 95% CI, e0.82 to e0.20) had slightly lower
mean mathematics test scores than children born vaginally without instruments, after adjustment for major confounders. Mean average grades in children delivered by vacuum extraction were e1.05 (95% CI, e1.87 to e0.23) and e1.20 (95% CI,e2.24 to e0.16) in children delivered by nonplanned cesarean section compared with children born vaginally. CONCLUSION: Children delivered by vacuum extraction had slightly
lower grades at age 16 years compared with those born by noninstrumental vaginal delivery but very similar to those delivered by nonplanned cesarean. This suggests that vacuum extraction and nonplanned cesarean are equivalent alternatives for terminating deliveries with respect to cognitive outcomes. Key words: cesarean section, cognitive development, mode of delivery, school grades, vacuum extraction
Cite this article as: Ahlberg M, Eke´us C, Hjern A. Birth by vacuum extraction delivery and school performance at 16 years of age. Am J Obstet Gynecol 2014;210:361.e1-8.
D
elivery by vacuum extraction is a common obstetrical procedure in the Western world, and in many countries it has replaced the use of forceps.1 Delivery by vacuum extraction has been associated with both mild and From the Division of Reproductive Health, Department of Women’s and Children’s Health, (Ms Ahlberg and Dr Ekéus), and the Division of Clinical Epidemiology, Department of Medicine, Karolinska Institute, and the Center for Health Equity Studies, Stockholm, Sweden (Dr Hjern). Received May 20, 2013; revised Sept. 25, 2013; accepted Nov. 6, 2013. The study was supported by grants from the Swedish Research Council. The authors report no conflict of interest. Presented in oral format at the First European Congress on Intrapartum Care, Amsterdam, The Netherlands, May 23-25, 2013. Reprints: Mia Ahlberg, RNM, Department of Women’s and Children’s Health, Division of Reproductive Health, Karolinska Institutet, Stockholm, Sweden 17176. [email protected]. 0002-9378/$36.00 ª 2014 Mosby, Inc. All rights reserved. http://dx.doi.org/10.1016/j.ajog.2013.11.015
severe acute complications for the infant. Mild complications include scalp edema, retinal hemorrhage, and cephalic hematoma. More serious complications include subgaleal hematoma, skull fractures, asphyxia, and intracranial hemorrhage.1-5 Despite the risk of cerebral complications, few studies have focused on long-term consequences for children delivered by vacuum extraction. The studies conducted have not shown a correlation between vacuum extraction delivery and impaired development, cerebral sequel, vision tests, and intelligence.6-9 However, a majority of these studies used small sample sizes and might be unrepresentative of the general population. Most studies also suffer from a short follow-up time and a lack of adjustment for major confounders. Large population-based studies involving long-term follow-ups are thus required. The aim of the present study was to investigate whether delivery by vacuum extraction influences the child’s cognitive competence in terms of school performance at 16 years of age.
M ATERIALS
AND
M ETHODS
This study was based on routinely collected data from Swedish national registers held by Statistics Sweden and the National Board of Health and Welfare. All Swedish residents are assigned a unique 10 digit identification number at birth or immigration. These identification numbers were used to link information from different register sources. The study was approved by the Regional Ethics Committee in Stockholm.
Study population The study cohort was identified in the Medical Birth Register and included all firstborn singleton infants of native Swedish parents, born after gestational week 34þ0 during the years 1990-1993. In 1990, Sweden introduced pregnancy dating by ultrasound as a routine, and children born after 1993 did not have their school grades forwarded to the National School Register. Children delivered before gestational week 34 were excluded because this is considered inappropriate use of vacuum extraction in Sweden. For the child to be included in
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the study, his or her mother had to be alive and a resident of Sweden when the child reached 15 years of age (n ¼ 148,881). From this population we excluded infants with a malformation with possible clinical significance (n ¼ 4558), infants delivered by forceps (n ¼ 1369), and those born in breech presentations (n ¼ 4399). Furthermore, we excluded children without a registered grade point average (n ¼ 4691) or mathematics test score (n ¼ 7832) at the age of 16 years. The definition of serious malformation was based on the diagnoses made by the attending pediatrician. It included all malformations with the exception of nondescended testicles, preauricular appendage, and minor malformations of fingers and toes. The study population of 126,032 children was followed up at 15-16 years of age, at graduation from compulsory school (at the end of ninth grade) between 2006 and 2009.
Exposure variables The exposure variables, modes of delivery, were collected from the Medical Birth Register and categorized into noninstrumental vaginal delivery, meaning a vaginal delivery without the use of any instrument, vacuum extraction, nonplanned cesarean section, and planned cesarean section. A cesarean section was defined as nonplanned if the operation was conducted after the onset of labor, either spontaneous or by induction, and defined as planned if it was performed before the onset of labor. Pregnancy, birth, and perinatal variables Information about the mother’s age at birth, mode of delivery, smoking habits in early pregnancy, maternal diseases, and complications during pregnancy and labor was collected from the Swedish Medical Birth Register, a national register with high-quality data on more than 99% of all births in Sweden.10 From the same register, perinatal data were collected about sex, gestational age, birthweight, and head circumference, whether the child was small for gestational age (SGA; 2 SD11); cephalic hematoma, intracranial bleeding, central nervous system complications, convulsions after birth, and Apgar scores at 5 minutes. Maternal diseases and pregnancy and labor complications, as well as neonatal diagnoses, were coded according to the International Classification of Diseases, ninth revision (ICD-9).12
Socioeconomic variables Data on parental education were collected from the Swedish Educational Register and defined as the highest formal education attained in the household 1 year before the child’s graduation. The educational level was categorized by years of education into less than 10 years (compulsory), 10-14 years (high school), and more than 14 (university). Data on social welfare recipiency and household disposable income were collected from the Total Enumeration Income Survey and was categorized into quintiles in which quintile 1 included the 20% of children in families with the lowest incomes. Residency was retrieved from the Register of the Total Population and categorized into big city, small city, and rural. Maternal morbidity Data from the Swedish Hospital Discharge Register 1973-2008 were used to create dichotomized variables associated with psychiatric and addictive disorders in the mother. Illicit drug and alcohol abuse (yes/no) indicates whether the mother had been discharged from a Swedish hospital with a diagnosis associated with use or abuse of alcohol or illicit drugs in ICD-9.12 Psychiatric disorder (yes/no) shows whether the mother had been discharged at least once from a Swedish hospital with a diagnosis in the psychiatric chapter in ICD-9.12 Outcome variables The study population was followed up at 15-16 years of age using 2 outcome variables: mean grade point average and the mean score on national mathematics tests. Data were collected from the National School Register kept by Statistics Sweden. The quality of the data in the National School Register is high, and
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summary statistics are published on a regular basis.13 The majority of all children (more than 90%) attend compulsory school, which lasts 9 years, usually between the ages of 7 and 16 years. The register contains information on all school grades at the final examinations and graduation grades for each pupil leaving Swedish compulsory school. From 1998 onward, the Swedish school system has used alphabetic grades with 4 levels: fail, pass, pass with distinction, and pass with special distinction. Grades are awarded on a 3-level scale: a pass is counted as 10 merit points, a pass with distinction as 15 merit points, and a pass with special distinction as 20 merit points. The maximum merit rating is 320 points. Before selection for upper secondary schools, the pupil’s final schoolleaving grade (ie, mean grade point average) is calculated as the sum of the points of the pupil’s 16 best grades on the leaving certificate. The second outcome, the mathematics test score, was based on the sum of 4 subsample national tests in mathematics that all pupils attending the final year of compulsory school write. The maximum mathematics test scores in the years 2003-2006 ranged from 68 to 75.
Statistical methods We conducted linear regression analyses using SPSS version 18.0 for Windows (SPSS Inc, Chicago, IL) to estimate crude and adjusted mean differences in mean grade points and mean mathematics grades with 95% confidence intervals in relation to mode of delivery. Noninstrumental vaginal delivery served as the reference group in the analyses. To control for potential confounders, we used the following 3 models: model 1 was adjusted for year of graduation and sex only. For model 2 we added the following socioeconomic, demographic, and maternal morbidity variables to the confounders in model 1; maternal age, highest educational level in the household 1 year before graduation, urban/rural residency 1 year before graduation, singleparent household, maternal smoking, maternal drug abuse, maternal alcohol abuse, and maternal psychiatric diagnosis were added in model 2. In the final model,
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TABLE 1
Perinatal, maternal, and sociodemographic characteristics in relation to mode of delivery NIVD, % (n [ 100,038)
VE, % (n [ 14,494)
NPCS, % (n [ 8753)
PC, % (n [ 2386)
VE plus EC, % (n [ 361)
64,577
49.9
57.1
56.3
51.6
58.4
34-36
5406
4.0
2.2
6.6
20.6
1.1
37-41
109,655
88.8
84.4
74.5
73.0
82.0
>42
10,971
7.2
13.4
18.9
6.5
16.9
32
9522
7.9
4.4
7.4
14.4
2.8
Study population (n [ 126,032)
n
Sex Male Gestational age, wks
Head circumference, cm 33-35
78,330
65.2
50.4
50.4
51.6
38.2
>36
34,408
24.4
41.4
36.5
27.5
48.8
3772
2.5
3.7
5.8
6.5
10.2
3209
1.6
9.7
1.1
0.7
21.1
13,314
10.5
9.9
11.7
13.0
9.1
30,156
23.8
23.8
25.1
25.5
19.1
10,938
6.9
9.2
20.8
34.3
10.5
6301
5.5
3.1
3.2
2.8
2.2
20-29
76,535
76.5
68.4
65.9
58.5
69.5
30-39
25,121
17.7
27.6
29.3
33.4
27.4
746
0.3
0.9
1.6
5.2
0.8
25,669
20.2
21.1
21.4
21.8
16.3
6447
5.1
4.9
5.5
5.9
5.8
Compulsory
12,722
10.1
9.9
10.5
11.2
8.6
High school
88,835
70.7
69.7
69.5
67.9
70.4
University
22,165
17.3
18.7
18.1
19.0
19.4
First quintile
15,069
12.4
11.3
10.8
12.0
11.8
Second quintile
20,209
16.3
16.4
16.2
16.6
15.2
Third quintile
24,794
20.1
19.5
20.2
18.3
18.3
Fourth quintile
30,613
24.9
24.0
24.1
23.6
27.8
Fifth quintile
33,115
26.2
28.7
28.6
29.6
27.0
Missing Neonatal complications
a
Yes Maternal psychiatric morbidity Yes
b
Single household Yes Pregnancy complications
c
Yes Maternal age, y 40 Smoking Yes Missing Highest educational level
Income
d
d
Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
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Perinatal, maternal, and sociodemographic characteristics in relation to mode of delivery (continued) Study population (n [ 126,032)
n
NIVD, % (n [ 100,038)
VE, % (n [ 14,494)
NPCS, % (n [ 8753)
PC, % (n [ 2386)
VE plus EC, % (n [ 361)
Residencyd Big city
50,695
39.8
41.9
42.0
40.1
37.4
Small city
53,687
42.7
42.3
40.8
43.9
46.3
Rural
21,650
17.4
15.8
17.2
16.0
16.3
NIVD, noninstrumental vaginal delivery; NPCS, nonplanned cesarean section; PC, planned cesarean section; VE, vacuum extraction; VE plus EC, vacuum extraction with a subsequent cesarean section. a
Cephalic hematoma, intracranial bleeding, convulsions, and other central nervous system disorders; b Drug abuse, alcohol abuse, and psychiatric diagnosis; c Gestational diabetes, maternal diabetes, preeclampsia, oligohydramnion, polyhydramnion, small for gestational age, and large for gestational age; d Registered at the child’s age of 14 years.
Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
we added potential medical confounders to the variables in model 2: SGA, LGA, oligohydramnion, polyhydramnion, maternal diabetes, preeclampsia, head circumference, and gestational age. To further control for residual perinatal confounding, subgroup analyses were conducted on a selected population of term children (gestational week >36), with Apgar score (>6) at 5 minutes, who were born without a diagnosis of fetal distress. The same linear regression models were used to test for the association mode of delivery and school grades (not shown in a table). Our main analyses are based on children who graduated from compulsory school with registered mean grade point averages and mathematics test results. The children with no available grade records were analyzed separately to assess possible selection bias.
R ESULTS The study population included 126,032 children: 11.5% were delivered by vacuum extraction, 7.0% by nonplanned cesarean, 1.9% by elective cesarean, 0.3% by vacuum extraction and subsequent cesarean, and 79.4% by noninstrumental vaginal delivery. From 1990 to 1993, deliveries by vacuum extraction increased from 10.5% to 12.6%, whereas nonplanned cesarean sections ranged between 6.9% and 7.5%. Mean mathematics test scores remained relatively stable over the years 1990-1993, ranging from 40.0 to 40.4. The mean grade point average increased from 218.8 in 1990 to 226.0 in 1993.
Table 1 shows maternal, perinatal, and sociodemographic characteristics of the study population in relation to mode of delivery. Women whose children were delivered by vacuum extraction were more likely to be older, to have a higher education, and to have a higher household income than women who gave birth vaginally without instruments. Of all children delivered by vacuum extraction, 2% had Apgar scores lower than 7 at 5 minutes. More boys (57.1%) than girls (42.9%) were delivered by vacuum extraction. Table 2 shows maternal, perinatal, and sociodemographic characteristics in relation to the crude mean mathematics test score and the crude mean grade point average. Differences in crude mean mathematics scores as well as in crude mean grade point averages were small in relation to mode of delivery. Children delivered by vacuum extraction had the highest crude mean mathematics test score (40.5), whereas the lowest score (40.2) was found among children delivered by noninstrumental vaginal delivery and nonplanned cesarean section. The highest crude mean grade point average was found in children delivered by planned cesarean section (225.4), and the lowest mean grade point average was found among children delivered by a vacuum extraction attempt followed by an acute cesarean section (222.9). Crude mean mathematics test scores and crude mean grade point averages rose increasingly with higher maternal age, higher education, and higher income level.
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Table 3 presents a linear regression analysis of the association between the mode of delivery and the mean mathematics test score. In model 1, after adjustments for the year of graduation and sex, children delivered by vacuum extraction scored 0.34 points higher than children born by noninstrumental vaginal delivery. In model 2, after we added all maternal and socioeconomic confounders, the children delivered by vacuum extraction showed lower mathematics test scores (e0.35) than children born by noninstrumental vaginal delivery. Maternal age was the confounder that most influenced the negative association. In the last model, when all perinatal, social, and maternal confounders were added, children delivered by vacuum extraction had lower scores (e0.51) than children born by noninstrumental delivery. Table 4 presents a linear regression model of the association between mode of delivery and mean grade point average. In model 1, after we adjusted for year of graduation and sex, the mean grade point average among children delivered by vacuum extraction was 2.12 points higher than that of children born by noninstrumental delivery. In model 2, after adding all maternal and socioeconomic confounders, children delivered by vacuum extraction had a lower mean grade point average (e0.77) than children born by noninstrumental delivery. In the last model, when all perinatal, social, and maternal confounders were
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TABLE 2
Sociodemographic, maternal, and perinatal characteristics in relation to mean mathematics test scores and mean grade point average Demographic, n [ 126,032
Mathematic scores, Mean (SD)
95% CI
Grade point average, Mean (SD)
95% CI
n ¼ 100,038
40.2 (14.9)
40.1e40.3
223.8 (52.4)
223.4e224.1
n ¼ 14,494
40.5 (14.9)
40.2e40.7
224.3 (52.3)
223.4e225.2
n ¼ 8753
40.2 (14.8)
39.9e40.5
223.1 (52.1)
222.01e224.2
n ¼ 2386
40.4 (14.8)
39.7e41.1
225.4 (52.0)
223.3e227.5
40.3 (15.0)
38.8e41.8
222.9 (52.0)
220.5e228.3
NIVD
VE
NPCS
PC
VE plus EC n ¼ 361 Sex Male
40.0 (14.9)
39.9e40.1
212.4 (50.5)
211.7e212.8
Female
40.5 (14.9)
40.4e40.6
235.8 (51.5)
235.4e236.2
34-36
39.6 (14.9)
39.2e40.0
220.9 (52.4)
219.5e222.3
37-41
40.2 (14.9)
40.1e40.3
223.9 (52.4)
223.6e224.2
>42
40.5 (14.8)
40.2e40.8
224.0 (51.7)
223.0e225.0
32
38.3 (14.8)
38.0e38.6
220.3 (52.7)
219.2e221.4
33-35
39.9 (14.9)
39.8e40.0
224.1 (52.4)
223.7e224.5
Gestational age, wks
Head circumference, cm
>36
41.5 (14.9)
41.3e41.7
224.4 (52.0)
223.9e224.9
Missing
39.9 (14.8)
39.4e40.4
221.4 (52.5)
219.7e223.1
39.8 (15.0)
38.9e40.7
220.4 (52.4)
217.3e223.5
39.8 (15.0)
39.0e40.7
222.5 (52.7)
219.5e225.5
39.3 (14.8)
38.8e39.8
219.5 (50.8)
217.7e221.3
36.4 (14.6)
36.2e36.7
206.2 (56.5)
205.2e207.2
37.3 (14.6)
37.1e37.5
209.7 (54.7)
209.1e210.3
36.9 (14.1)
36.3e37.5
212.3 (55.8)
210.0e214.6
39.2 (15.0)
38.9e39.5
219.8 (52.7)
218.8e220.8
>19
32.1 (13.1)
31.8e32.4
186.3 (52.6)
185.0e187.6
20-29
39.7 (14.8)
39.6e39.8
221.9 (51.3)
221.6e222.2
Low Apgar 5 minutes Yes Missing Neonatal complications
a
Yes Maternal psychiatric morbidity Yes
b
Single-parent household Yes Missing Pregnancy complications Yes
c
Maternal age, y
Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
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TABLE 2
Sociodemographic, maternal, and perinatal characteristics in relation to mean mathematics test scores and mean grade point average (continued) Demographic, n [ 126,032
Mathematic scores, Mean (SD)
95% CI
Grade point average, Mean (SD)
95% CI
30-39
44.2 (14.9)
44.0e44.4
239.8 (50.2)
239.2e240.4
>40
44.2 (14.9)
43.2e45.3
241.4 (51.0)
237.7e245.1
35.3 (14.1)
35.1e35.5
203.1 (53.7)
202.5e203.7
39.3 (14.8)
39.0e39.7
220.2 (51.8)
218.9e221.5
35.1 (13.9)
34.9e35.3
202.4 (52.4)
201.5e203.3
Smoking Yes Missing Highest educational level Compulsory
d
High school
39.1 (14.5)
39.0e39.2
220.2 (50.7)
219.9e220.5
University
47.9 (14.4)
47.7e48.1
251.8 (47.6)
251.2e252.4
First quintile
37.1 (14.3)
36.9e37.3
211.5 (52.9)
210.7e212.3
Second quintile
37.5 (14.3)
37.3e37.7
213.9 (53.0)
213.2e214.6
Third quintile
38.5 (14.6)
38.3e38.7
217.1 (52.3)
216.4e217.8
Incomed
Fourth quintile
40.0 (14.7)
39.8e40.2
223.3 (49.9)
222.7e223.9
Fifth quintile
45.1 (14.9)
44.9e45.3
241.7 (48.9)
241.2e242.2
Residencyd Big city
42.0 (15.0)
41.9e42.1
230.3 (53.3)
229.8e230.8
Small city
39.4 (14.8)
39.3e39.5
220.3 (51.3)
219.9e220.7
Rural
38.0 (14.6)
37.8e38.2
217.2 (52.3)
216.5e217.9
NIVD, noninstrumental vaginal delivery; NPCS, nonplanned cesarean section; PC, planned cesarean section; VE, vacuum extraction; VE plus EC, vacuum extraction with a subsequent cesarean section. a
Cephalic hematoma, intracranial bleeding, convulsions, and other central nervous system disorders; b Drug abuse, alcohol abuse, and psychiatric diagnosis; c Gestational diabetes, maternal diabetes, preeclampsia, oligohydramnion, polyhydramnion, small for gestational age, and large for gestational age; d Registered at the child’s age of 14 years.
Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
added, children delivered by vacuum extraction had (e1.05) lower scores, compared with children born by noninstrumental delivery. Overall, children born by noninstrumental delivery had the highest mean grade point average and mean mathematics test score compared with all other modes of delivery. When the analyses (using the same models) were restricted to term children and with an Apgar score of 7 or greater at 5 minutes and without a diagnosis of fetal distress (not shown in a table), the results showed the same pattern as that in Tables 3 and 4. Compared with children born by noninstrumental vaginal delivery, those delivered by vacuum extraction had a slightly higher mean
mathematics test score (þ0.47; 95% confidence interval [CI], 0.14e0.80) and mean grade point average (þ1.57; 95% CI, 0.43e2.73), after adjusting for year of graduation and sex. When the perinatal, maternal, and social confounders were added, children delivered by vacuum extraction had e0.47 (95% CI, e0.78 to e0.15) mean mathematics test score and e0.74 (95% CI, e1.77 to e0.30) mean grade point average. The odds of having no registered mathematics test scores or no registered merit grade were 0.99 (95% CI, 0.91e1.08) and 0.70 (95% CI, 0.58e0.86) for children delivered by vacuum extraction compared with those delivered without a vacuum extraction, respectively.
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C OMMENT In this national cohort study of 126,032 children, we found that both vacuum extraction delivery and nonplanned cesarean section were associated with a slight decrease in both mean mathematics test score and mean grade point average at 16 years of age, compared with noninstrumental vaginal delivery. Expressed as standard mean differences, the effect sizes of vacuum extraction compared with noninstrumental vaginal delivery, however, were only 0.08 for mathematics test and 0.09 for mean grade average, which are marginal effects according to the criteria suggested by Cohen,14 in which effects between 0.20 and 0.40 are considered small.
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TABLE 3
Linear regression for mean mathematics test score in relation to mode of delivery Model 1
Model 2
MOD
Mean
b
(95% CI)
b
NIVD
40.2
Referent
VE
40.5
0.34
(0.08e0.60)
e0.35
(e0.60 to e0.11)
e0.51
(e0.76 to e0.26)
VE plus EC
40.3
0.26
(e1.28 to 1.80)
e0.83
(e2.27 to 0.61)
e1.08
(e2.52 to 0.36)
NPCS
40.2
0.02
(e0.30 to 0.35)
e0.50
(e0.81 to e0.19)
e0.51
(e0.82 to e0.20)
PC
40.4
0.27
(e0.33 to 0.87)
e0.54
(e1.11 to e0.03)
e0.51
(e1.10 to 0.08)
(95% CI)
b
Model 3
Referent
(95% CI)
Referent
Model 1: year of graduation and sex; model 2: same as model 1, adding maternal age, educational level and residency, single-parent household, maternal smoking, maternal drug abuse, maternal alcohol abuse, and maternal psychiatric diagnosis; model 3: same as previous 2 models, adding small for gestational age, large for gestational age, oligohydramnion, polyhydramnion, maternal diabetes, preeclampsia, head circumference, and gestational age. CI, confidence interval; MOD, mode of delivery; NIVD, noninstrumental vaginal delivery; NPCS, nonplanned cesarean section; PC, planned cesarean section; VE, vacuum extraction; VE plus EC, vacuum extraction and subsequent cesarean section. Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
These differences, which were very similar for vacuum extraction and nonplanned cesarean, cannot be expected to have anything but a minimal impact on the life course of these individuals. Furthermore, our results suggest that vacuum extraction and nonplanned cesarean section are equivalent alternatives for terminating deliveries with respect to cognitive outcomes. No previous studies have shown an association between vacuum extraction delivery and various adverse long-term health outcomes.5-8 One large populationbased study comparable with ours found no effects of mode of delivery on intelligence scores among children at 17 years of age.15 Considering that the observed differences in our study were small, we
believe that these 2 studies could be interpreted in a similar vein. Thus, our results suggest that vacuum extraction is quite a safe method of delivery with respect to cognitive outcomes. It should be noted that this study was conducted in a country with a relatively high rate of vacuum extraction from an international perspective, and therefore, most operators have a high level of experience. It has been shown that a lack of operator experience is related to adverse neonatal outcomes in vacuum extractions.16,17 Our results can therefore not automatically be generalized to settings in which vacuum extraction is a rare choice for terminating a delivery. A major strength of this study is its nationwide population-based design
along with the possibility of acquiring information on confounders through different registers. Information on exposure, outcomes, and potential confounders was collected independently and without involving the study subjects, thus minimizing various types of bias (eg, selection, recall). We excluded 12,523 children from the study because they had not graduated from compulsory school. No indication arose in separate analyses of this group that the exclusion biased our results. Although many potential perinatal confounders were present in the register, many of these have to be considered low-precision proxies for the underlying risk factors, such as asphyxia, thus
TABLE 4
Linear regression for mean grade point average in relation to mode of delivery Model 1 MOD
Mean
b
NIVD
223.8
Referent
Model 2 (95% CI)
b
Model 3 (95% CI)
Referent
b
(95% CI)
Referent
VE
224.3
2.12
(1.23e3.01)
e0.77
(e1.59 to 0.04)
e1.05
(e1.87 to e0.23)
VE plus EC
222.9
1.03
(e4.24 to 6.29)
e3.96
(e8.75 to 0.83)
e4.30
(e9.10 to 0.49)
NPCS
223.1
0.73
(e0.39 to 1.84)
e1.47
(e2.50 to e0.45)
e1.20
(e2.24 to e0.16)
PC
225.4
2.08
(0.01e4.15)
e1.43
(e3.33 to 0.47)
e0.90
(e2.85 to 1.05)
Model 1: year of graduation and sex; model 2: same as model 1, adding maternal age, educational level and residency, single-parent household, maternal smoking, maternal drug abuse, maternal alcohol abuse, and maternal psychiatric diagnosis; model 3: same as models 1 and 2, adding small for gestational age, large for gestational age, oligohydramnion, polyhydramnion, maternal diabetes, preeclampsia, head circumference, and gestational age. CI, confidence interval; MOD, mode of delivery; NIVD, noninstrumental vaginal delivery; NPCS, nonplanned cesarean section; PC, planned cesarean section; VE, vacuum extraction; VE plus EC, vacuum extraction and subsequent cesarean section. Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
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making residual perinatal confounding an important concern in the interpretation of our results.
Conclusion Both delivery by vacuum extraction and delivery by nonplanned cesarean section are associated with a marginally lower school performance at 16 years of age, compared with noninstrumental vaginal delivery. The differences, however, are so small that it probably has no impact or only a minimal impact on the life course of a child. This study indicates that delivery by vacuum extraction is quite safe for children from a long-term perspective. REFERENCES 1. Miksovsky P, Watson WJ. Obstetric vacuum extraction: state of the art in the new millennium. Obstet Gynecol Surv 2001;56: 736-51. 2. Edozien LC. Towards safe practice in instrumental vaginal delivery. Best Pract Res Clin Obstet Gynaecol 2007;21:639-55.
www.AJOG.org 3. Simonson C, Barlow P, Dehennin N, et al. Neonatal complications of vacuum-assisted delivery. Obstet Gynecol 2007;109:626-33. 4. Doumouchtsis SK, Arulkumaran S. Head injuries after instrumental vaginal deliveries. Curr Opin Obstet Gynecol 2006;18:129-34. 5. Wen SW, Liu S, Kramer MS, et al. Comparison of maternal and infant outcomes between vacuum extraction and forceps deliveries. Am J Epidemiol 2001;153:103-7. 6. Ngan HY, Miu P, Ko L, Ma HK. Long-term neurological sequelae following vacuum extractor delivery. Aust N Z J Obstet Gynaecol 1990;30:111-4. 7. Blennow G, Svenningsen NW, Gustafson B, Sunden B, Cronquist S. Neonatal and prospective follow-up study of infants delivered by vacuum extraction (VE). Acta Obstet Gynecol Scand 1977;56:189-94. 8. Johanson RB, Heycock E, Carter J, Sultan AH, Walklate K, Jones PW. Maternal and child health after assisted vaginal delivery: fiveyear follow up of a randomised controlled study comparing forceps and ventouse. Br J Obstet Gynaecol 1999;106:544-9. 9. Carmody F, Grant A, Mutch L, Vacca A, Chalmers I. Follow up of babies delivered in a randomized controlled comparison of vacuum extraction and forceps delivery. Acta Obstet Gynecol Scand 1986;65:763-6.
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10. Cnattingius S, Ericson A, Gunnarskog J, Kallen B. A quality study of a medical birth registry. Scand J Soc Med 1990;18:143-8. 11. Marsal K, Persson PH, Larsen T, Lilja H, Selbing A, Sultan B. Intrauterine growth curves based on ultrasonically estimated foetal weights. Acta Paediatr 1996;85:843-8. 12. World Health Organisation. International classification of disorders, 9th ed. Geneva (Switzerland): World Health Organisation; 1986. 13. Swedish National Agency for Education web site. Available at: http://www.skolverket.se/ statistik-och-utvardering/statistik/grundskola/ betyg/betyg-i-grundskolan-lasar-2010-11-1. 160176. Accessed Aug. 30, 2013. 14. Cohen JA. power primer. Psychol Bull 1992;112:155-9. 15. Seidman DS, Laor A, Gale R, Stevenson DK, Mashiach S, Danon YL. Long-term effects of vacuum and forceps deliveries. Lancet 1991;337:1583-5. 16. Murphy DJ, Liebling RE, Patel R, Verity L, Swingler R. Cohort study of operative delivery in the second stage of labour and standard of obstetric care. BJOG 2003;110:610-5. 17. Cheong YC, Abdullahi H, Lashen H, Fairlie FM. Can formal education and training improve the outcome of instrumental delivery? Eur J Obstet Gynecol Reprod Biol 2004;113: 139-44.
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OBSTETRICS
Birth by vacuum extraction delivery and school performance at 16 years of age Mia Ahlberg, RNM; Cecilia Eke´us, PhD; Anders Hjern, PhD OBJECTIVE: The aim of the present study was to investigate cognitive competence, as indicated by school performance, at 16 years of age, in children delivered by vacuum extraction. STUDY DESIGN: This was a register study of a national cohort of 126,032 16 year olds born as singletons, with a vertex presentation, at a gestational age of 34 weeks or older, with Swedish-born parents, delivered between 1990 and 1993 without major congenital malformations. Linear regression was used to analyze mode of delivery in relation to mean scores from national tests in mathematics (40.2; scale, 10-75; SD, 14.9) and mean average grades (223.8; scale, 10-320; SD, 52.3), with adjustment for perinatal and sociodemographic confounders. RESULTS: Children delivered by vacuum extraction (e0.51; 95% confidence interval [CI], e0.76 to 0.26) as well as by nonplanned cesarean section (e0.51; 95% CI, e0.82 to e0.20) had slightly lower
mean mathematics test scores than children born vaginally without instruments, after adjustment for major confounders. Mean average grades in children delivered by vacuum extraction were e1.05 (95% CI, e1.87 to e0.23) and e1.20 (95% CI,e2.24 to e0.16) in children delivered by nonplanned cesarean section compared with children born vaginally. CONCLUSION: Children delivered by vacuum extraction had slightly
lower grades at age 16 years compared with those born by noninstrumental vaginal delivery but very similar to those delivered by nonplanned cesarean. This suggests that vacuum extraction and nonplanned cesarean are equivalent alternatives for terminating deliveries with respect to cognitive outcomes. Key words: cesarean section, cognitive development, mode of delivery, school grades, vacuum extraction
Cite this article as: Ahlberg M, Eke´us C, Hjern A. Birth by vacuum extraction delivery and school performance at 16 years of age. Am J Obstet Gynecol 2014;210:361.e1-8.
D
elivery by vacuum extraction is a common obstetrical procedure in the Western world, and in many countries it has replaced the use of forceps.1 Delivery by vacuum extraction has been associated with both mild and From the Division of Reproductive Health, Department of Women’s and Children’s Health, (Ms Ahlberg and Dr Ekéus), and the Division of Clinical Epidemiology, Department of Medicine, Karolinska Institute, and the Center for Health Equity Studies, Stockholm, Sweden (Dr Hjern). Received May 20, 2013; revised Sept. 25, 2013; accepted Nov. 6, 2013. The study was supported by grants from the Swedish Research Council. The authors report no conflict of interest. Presented in oral format at the First European Congress on Intrapartum Care, Amsterdam, The Netherlands, May 23-25, 2013. Reprints: Mia Ahlberg, RNM, Department of Women’s and Children’s Health, Division of Reproductive Health, Karolinska Institutet, Stockholm, Sweden 17176. [email protected]. 0002-9378/$36.00 ª 2014 Mosby, Inc. All rights reserved. http://dx.doi.org/10.1016/j.ajog.2013.11.015
severe acute complications for the infant. Mild complications include scalp edema, retinal hemorrhage, and cephalic hematoma. More serious complications include subgaleal hematoma, skull fractures, asphyxia, and intracranial hemorrhage.1-5 Despite the risk of cerebral complications, few studies have focused on long-term consequences for children delivered by vacuum extraction. The studies conducted have not shown a correlation between vacuum extraction delivery and impaired development, cerebral sequel, vision tests, and intelligence.6-9 However, a majority of these studies used small sample sizes and might be unrepresentative of the general population. Most studies also suffer from a short follow-up time and a lack of adjustment for major confounders. Large population-based studies involving long-term follow-ups are thus required. The aim of the present study was to investigate whether delivery by vacuum extraction influences the child’s cognitive competence in terms of school performance at 16 years of age.
M ATERIALS
AND
M ETHODS
This study was based on routinely collected data from Swedish national registers held by Statistics Sweden and the National Board of Health and Welfare. All Swedish residents are assigned a unique 10 digit identification number at birth or immigration. These identification numbers were used to link information from different register sources. The study was approved by the Regional Ethics Committee in Stockholm.
Study population The study cohort was identified in the Medical Birth Register and included all firstborn singleton infants of native Swedish parents, born after gestational week 34þ0 during the years 1990-1993. In 1990, Sweden introduced pregnancy dating by ultrasound as a routine, and children born after 1993 did not have their school grades forwarded to the National School Register. Children delivered before gestational week 34 were excluded because this is considered inappropriate use of vacuum extraction in Sweden. For the child to be included in
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the study, his or her mother had to be alive and a resident of Sweden when the child reached 15 years of age (n ¼ 148,881). From this population we excluded infants with a malformation with possible clinical significance (n ¼ 4558), infants delivered by forceps (n ¼ 1369), and those born in breech presentations (n ¼ 4399). Furthermore, we excluded children without a registered grade point average (n ¼ 4691) or mathematics test score (n ¼ 7832) at the age of 16 years. The definition of serious malformation was based on the diagnoses made by the attending pediatrician. It included all malformations with the exception of nondescended testicles, preauricular appendage, and minor malformations of fingers and toes. The study population of 126,032 children was followed up at 15-16 years of age, at graduation from compulsory school (at the end of ninth grade) between 2006 and 2009.
Exposure variables The exposure variables, modes of delivery, were collected from the Medical Birth Register and categorized into noninstrumental vaginal delivery, meaning a vaginal delivery without the use of any instrument, vacuum extraction, nonplanned cesarean section, and planned cesarean section. A cesarean section was defined as nonplanned if the operation was conducted after the onset of labor, either spontaneous or by induction, and defined as planned if it was performed before the onset of labor. Pregnancy, birth, and perinatal variables Information about the mother’s age at birth, mode of delivery, smoking habits in early pregnancy, maternal diseases, and complications during pregnancy and labor was collected from the Swedish Medical Birth Register, a national register with high-quality data on more than 99% of all births in Sweden.10 From the same register, perinatal data were collected about sex, gestational age, birthweight, and head circumference, whether the child was small for gestational age (SGA; 2 SD11); cephalic hematoma, intracranial bleeding, central nervous system complications, convulsions after birth, and Apgar scores at 5 minutes. Maternal diseases and pregnancy and labor complications, as well as neonatal diagnoses, were coded according to the International Classification of Diseases, ninth revision (ICD-9).12
Socioeconomic variables Data on parental education were collected from the Swedish Educational Register and defined as the highest formal education attained in the household 1 year before the child’s graduation. The educational level was categorized by years of education into less than 10 years (compulsory), 10-14 years (high school), and more than 14 (university). Data on social welfare recipiency and household disposable income were collected from the Total Enumeration Income Survey and was categorized into quintiles in which quintile 1 included the 20% of children in families with the lowest incomes. Residency was retrieved from the Register of the Total Population and categorized into big city, small city, and rural. Maternal morbidity Data from the Swedish Hospital Discharge Register 1973-2008 were used to create dichotomized variables associated with psychiatric and addictive disorders in the mother. Illicit drug and alcohol abuse (yes/no) indicates whether the mother had been discharged from a Swedish hospital with a diagnosis associated with use or abuse of alcohol or illicit drugs in ICD-9.12 Psychiatric disorder (yes/no) shows whether the mother had been discharged at least once from a Swedish hospital with a diagnosis in the psychiatric chapter in ICD-9.12 Outcome variables The study population was followed up at 15-16 years of age using 2 outcome variables: mean grade point average and the mean score on national mathematics tests. Data were collected from the National School Register kept by Statistics Sweden. The quality of the data in the National School Register is high, and
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summary statistics are published on a regular basis.13 The majority of all children (more than 90%) attend compulsory school, which lasts 9 years, usually between the ages of 7 and 16 years. The register contains information on all school grades at the final examinations and graduation grades for each pupil leaving Swedish compulsory school. From 1998 onward, the Swedish school system has used alphabetic grades with 4 levels: fail, pass, pass with distinction, and pass with special distinction. Grades are awarded on a 3-level scale: a pass is counted as 10 merit points, a pass with distinction as 15 merit points, and a pass with special distinction as 20 merit points. The maximum merit rating is 320 points. Before selection for upper secondary schools, the pupil’s final schoolleaving grade (ie, mean grade point average) is calculated as the sum of the points of the pupil’s 16 best grades on the leaving certificate. The second outcome, the mathematics test score, was based on the sum of 4 subsample national tests in mathematics that all pupils attending the final year of compulsory school write. The maximum mathematics test scores in the years 2003-2006 ranged from 68 to 75.
Statistical methods We conducted linear regression analyses using SPSS version 18.0 for Windows (SPSS Inc, Chicago, IL) to estimate crude and adjusted mean differences in mean grade points and mean mathematics grades with 95% confidence intervals in relation to mode of delivery. Noninstrumental vaginal delivery served as the reference group in the analyses. To control for potential confounders, we used the following 3 models: model 1 was adjusted for year of graduation and sex only. For model 2 we added the following socioeconomic, demographic, and maternal morbidity variables to the confounders in model 1; maternal age, highest educational level in the household 1 year before graduation, urban/rural residency 1 year before graduation, singleparent household, maternal smoking, maternal drug abuse, maternal alcohol abuse, and maternal psychiatric diagnosis were added in model 2. In the final model,
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TABLE 1
Perinatal, maternal, and sociodemographic characteristics in relation to mode of delivery NIVD, % (n [ 100,038)
VE, % (n [ 14,494)
NPCS, % (n [ 8753)
PC, % (n [ 2386)
VE plus EC, % (n [ 361)
64,577
49.9
57.1
56.3
51.6
58.4
34-36
5406
4.0
2.2
6.6
20.6
1.1
37-41
109,655
88.8
84.4
74.5
73.0
82.0
>42
10,971
7.2
13.4
18.9
6.5
16.9
32
9522
7.9
4.4
7.4
14.4
2.8
Study population (n [ 126,032)
n
Sex Male Gestational age, wks
Head circumference, cm 33-35
78,330
65.2
50.4
50.4
51.6
38.2
>36
34,408
24.4
41.4
36.5
27.5
48.8
3772
2.5
3.7
5.8
6.5
10.2
3209
1.6
9.7
1.1
0.7
21.1
13,314
10.5
9.9
11.7
13.0
9.1
30,156
23.8
23.8
25.1
25.5
19.1
10,938
6.9
9.2
20.8
34.3
10.5
6301
5.5
3.1
3.2
2.8
2.2
20-29
76,535
76.5
68.4
65.9
58.5
69.5
30-39
25,121
17.7
27.6
29.3
33.4
27.4
746
0.3
0.9
1.6
5.2
0.8
25,669
20.2
21.1
21.4
21.8
16.3
6447
5.1
4.9
5.5
5.9
5.8
Compulsory
12,722
10.1
9.9
10.5
11.2
8.6
High school
88,835
70.7
69.7
69.5
67.9
70.4
University
22,165
17.3
18.7
18.1
19.0
19.4
First quintile
15,069
12.4
11.3
10.8
12.0
11.8
Second quintile
20,209
16.3
16.4
16.2
16.6
15.2
Third quintile
24,794
20.1
19.5
20.2
18.3
18.3
Fourth quintile
30,613
24.9
24.0
24.1
23.6
27.8
Fifth quintile
33,115
26.2
28.7
28.6
29.6
27.0
Missing Neonatal complications
a
Yes Maternal psychiatric morbidity Yes
b
Single household Yes Pregnancy complications
c
Yes Maternal age, y 40 Smoking Yes Missing Highest educational level
Income
d
d
Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
(continued)
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TABLE 1
Perinatal, maternal, and sociodemographic characteristics in relation to mode of delivery (continued) Study population (n [ 126,032)
n
NIVD, % (n [ 100,038)
VE, % (n [ 14,494)
NPCS, % (n [ 8753)
PC, % (n [ 2386)
VE plus EC, % (n [ 361)
Residencyd Big city
50,695
39.8
41.9
42.0
40.1
37.4
Small city
53,687
42.7
42.3
40.8
43.9
46.3
Rural
21,650
17.4
15.8
17.2
16.0
16.3
NIVD, noninstrumental vaginal delivery; NPCS, nonplanned cesarean section; PC, planned cesarean section; VE, vacuum extraction; VE plus EC, vacuum extraction with a subsequent cesarean section. a
Cephalic hematoma, intracranial bleeding, convulsions, and other central nervous system disorders; b Drug abuse, alcohol abuse, and psychiatric diagnosis; c Gestational diabetes, maternal diabetes, preeclampsia, oligohydramnion, polyhydramnion, small for gestational age, and large for gestational age; d Registered at the child’s age of 14 years.
Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
we added potential medical confounders to the variables in model 2: SGA, LGA, oligohydramnion, polyhydramnion, maternal diabetes, preeclampsia, head circumference, and gestational age. To further control for residual perinatal confounding, subgroup analyses were conducted on a selected population of term children (gestational week >36), with Apgar score (>6) at 5 minutes, who were born without a diagnosis of fetal distress. The same linear regression models were used to test for the association mode of delivery and school grades (not shown in a table). Our main analyses are based on children who graduated from compulsory school with registered mean grade point averages and mathematics test results. The children with no available grade records were analyzed separately to assess possible selection bias.
R ESULTS The study population included 126,032 children: 11.5% were delivered by vacuum extraction, 7.0% by nonplanned cesarean, 1.9% by elective cesarean, 0.3% by vacuum extraction and subsequent cesarean, and 79.4% by noninstrumental vaginal delivery. From 1990 to 1993, deliveries by vacuum extraction increased from 10.5% to 12.6%, whereas nonplanned cesarean sections ranged between 6.9% and 7.5%. Mean mathematics test scores remained relatively stable over the years 1990-1993, ranging from 40.0 to 40.4. The mean grade point average increased from 218.8 in 1990 to 226.0 in 1993.
Table 1 shows maternal, perinatal, and sociodemographic characteristics of the study population in relation to mode of delivery. Women whose children were delivered by vacuum extraction were more likely to be older, to have a higher education, and to have a higher household income than women who gave birth vaginally without instruments. Of all children delivered by vacuum extraction, 2% had Apgar scores lower than 7 at 5 minutes. More boys (57.1%) than girls (42.9%) were delivered by vacuum extraction. Table 2 shows maternal, perinatal, and sociodemographic characteristics in relation to the crude mean mathematics test score and the crude mean grade point average. Differences in crude mean mathematics scores as well as in crude mean grade point averages were small in relation to mode of delivery. Children delivered by vacuum extraction had the highest crude mean mathematics test score (40.5), whereas the lowest score (40.2) was found among children delivered by noninstrumental vaginal delivery and nonplanned cesarean section. The highest crude mean grade point average was found in children delivered by planned cesarean section (225.4), and the lowest mean grade point average was found among children delivered by a vacuum extraction attempt followed by an acute cesarean section (222.9). Crude mean mathematics test scores and crude mean grade point averages rose increasingly with higher maternal age, higher education, and higher income level.
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Table 3 presents a linear regression analysis of the association between the mode of delivery and the mean mathematics test score. In model 1, after adjustments for the year of graduation and sex, children delivered by vacuum extraction scored 0.34 points higher than children born by noninstrumental vaginal delivery. In model 2, after we added all maternal and socioeconomic confounders, the children delivered by vacuum extraction showed lower mathematics test scores (e0.35) than children born by noninstrumental vaginal delivery. Maternal age was the confounder that most influenced the negative association. In the last model, when all perinatal, social, and maternal confounders were added, children delivered by vacuum extraction had lower scores (e0.51) than children born by noninstrumental delivery. Table 4 presents a linear regression model of the association between mode of delivery and mean grade point average. In model 1, after we adjusted for year of graduation and sex, the mean grade point average among children delivered by vacuum extraction was 2.12 points higher than that of children born by noninstrumental delivery. In model 2, after adding all maternal and socioeconomic confounders, children delivered by vacuum extraction had a lower mean grade point average (e0.77) than children born by noninstrumental delivery. In the last model, when all perinatal, social, and maternal confounders were
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TABLE 2
Sociodemographic, maternal, and perinatal characteristics in relation to mean mathematics test scores and mean grade point average Demographic, n [ 126,032
Mathematic scores, Mean (SD)
95% CI
Grade point average, Mean (SD)
95% CI
n ¼ 100,038
40.2 (14.9)
40.1e40.3
223.8 (52.4)
223.4e224.1
n ¼ 14,494
40.5 (14.9)
40.2e40.7
224.3 (52.3)
223.4e225.2
n ¼ 8753
40.2 (14.8)
39.9e40.5
223.1 (52.1)
222.01e224.2
n ¼ 2386
40.4 (14.8)
39.7e41.1
225.4 (52.0)
223.3e227.5
40.3 (15.0)
38.8e41.8
222.9 (52.0)
220.5e228.3
NIVD
VE
NPCS
PC
VE plus EC n ¼ 361 Sex Male
40.0 (14.9)
39.9e40.1
212.4 (50.5)
211.7e212.8
Female
40.5 (14.9)
40.4e40.6
235.8 (51.5)
235.4e236.2
34-36
39.6 (14.9)
39.2e40.0
220.9 (52.4)
219.5e222.3
37-41
40.2 (14.9)
40.1e40.3
223.9 (52.4)
223.6e224.2
>42
40.5 (14.8)
40.2e40.8
224.0 (51.7)
223.0e225.0
32
38.3 (14.8)
38.0e38.6
220.3 (52.7)
219.2e221.4
33-35
39.9 (14.9)
39.8e40.0
224.1 (52.4)
223.7e224.5
Gestational age, wks
Head circumference, cm
>36
41.5 (14.9)
41.3e41.7
224.4 (52.0)
223.9e224.9
Missing
39.9 (14.8)
39.4e40.4
221.4 (52.5)
219.7e223.1
39.8 (15.0)
38.9e40.7
220.4 (52.4)
217.3e223.5
39.8 (15.0)
39.0e40.7
222.5 (52.7)
219.5e225.5
39.3 (14.8)
38.8e39.8
219.5 (50.8)
217.7e221.3
36.4 (14.6)
36.2e36.7
206.2 (56.5)
205.2e207.2
37.3 (14.6)
37.1e37.5
209.7 (54.7)
209.1e210.3
36.9 (14.1)
36.3e37.5
212.3 (55.8)
210.0e214.6
39.2 (15.0)
38.9e39.5
219.8 (52.7)
218.8e220.8
>19
32.1 (13.1)
31.8e32.4
186.3 (52.6)
185.0e187.6
20-29
39.7 (14.8)
39.6e39.8
221.9 (51.3)
221.6e222.2
Low Apgar 5 minutes Yes Missing Neonatal complications
a
Yes Maternal psychiatric morbidity Yes
b
Single-parent household Yes Missing Pregnancy complications Yes
c
Maternal age, y
Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
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TABLE 2
Sociodemographic, maternal, and perinatal characteristics in relation to mean mathematics test scores and mean grade point average (continued) Demographic, n [ 126,032
Mathematic scores, Mean (SD)
95% CI
Grade point average, Mean (SD)
95% CI
30-39
44.2 (14.9)
44.0e44.4
239.8 (50.2)
239.2e240.4
>40
44.2 (14.9)
43.2e45.3
241.4 (51.0)
237.7e245.1
35.3 (14.1)
35.1e35.5
203.1 (53.7)
202.5e203.7
39.3 (14.8)
39.0e39.7
220.2 (51.8)
218.9e221.5
35.1 (13.9)
34.9e35.3
202.4 (52.4)
201.5e203.3
Smoking Yes Missing Highest educational level Compulsory
d
High school
39.1 (14.5)
39.0e39.2
220.2 (50.7)
219.9e220.5
University
47.9 (14.4)
47.7e48.1
251.8 (47.6)
251.2e252.4
First quintile
37.1 (14.3)
36.9e37.3
211.5 (52.9)
210.7e212.3
Second quintile
37.5 (14.3)
37.3e37.7
213.9 (53.0)
213.2e214.6
Third quintile
38.5 (14.6)
38.3e38.7
217.1 (52.3)
216.4e217.8
Incomed
Fourth quintile
40.0 (14.7)
39.8e40.2
223.3 (49.9)
222.7e223.9
Fifth quintile
45.1 (14.9)
44.9e45.3
241.7 (48.9)
241.2e242.2
Residencyd Big city
42.0 (15.0)
41.9e42.1
230.3 (53.3)
229.8e230.8
Small city
39.4 (14.8)
39.3e39.5
220.3 (51.3)
219.9e220.7
Rural
38.0 (14.6)
37.8e38.2
217.2 (52.3)
216.5e217.9
NIVD, noninstrumental vaginal delivery; NPCS, nonplanned cesarean section; PC, planned cesarean section; VE, vacuum extraction; VE plus EC, vacuum extraction with a subsequent cesarean section. a
Cephalic hematoma, intracranial bleeding, convulsions, and other central nervous system disorders; b Drug abuse, alcohol abuse, and psychiatric diagnosis; c Gestational diabetes, maternal diabetes, preeclampsia, oligohydramnion, polyhydramnion, small for gestational age, and large for gestational age; d Registered at the child’s age of 14 years.
Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
added, children delivered by vacuum extraction had (e1.05) lower scores, compared with children born by noninstrumental delivery. Overall, children born by noninstrumental delivery had the highest mean grade point average and mean mathematics test score compared with all other modes of delivery. When the analyses (using the same models) were restricted to term children and with an Apgar score of 7 or greater at 5 minutes and without a diagnosis of fetal distress (not shown in a table), the results showed the same pattern as that in Tables 3 and 4. Compared with children born by noninstrumental vaginal delivery, those delivered by vacuum extraction had a slightly higher mean
mathematics test score (þ0.47; 95% confidence interval [CI], 0.14e0.80) and mean grade point average (þ1.57; 95% CI, 0.43e2.73), after adjusting for year of graduation and sex. When the perinatal, maternal, and social confounders were added, children delivered by vacuum extraction had e0.47 (95% CI, e0.78 to e0.15) mean mathematics test score and e0.74 (95% CI, e1.77 to e0.30) mean grade point average. The odds of having no registered mathematics test scores or no registered merit grade were 0.99 (95% CI, 0.91e1.08) and 0.70 (95% CI, 0.58e0.86) for children delivered by vacuum extraction compared with those delivered without a vacuum extraction, respectively.
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C OMMENT In this national cohort study of 126,032 children, we found that both vacuum extraction delivery and nonplanned cesarean section were associated with a slight decrease in both mean mathematics test score and mean grade point average at 16 years of age, compared with noninstrumental vaginal delivery. Expressed as standard mean differences, the effect sizes of vacuum extraction compared with noninstrumental vaginal delivery, however, were only 0.08 for mathematics test and 0.09 for mean grade average, which are marginal effects according to the criteria suggested by Cohen,14 in which effects between 0.20 and 0.40 are considered small.
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TABLE 3
Linear regression for mean mathematics test score in relation to mode of delivery Model 1
Model 2
MOD
Mean
b
(95% CI)
b
NIVD
40.2
Referent
VE
40.5
0.34
(0.08e0.60)
e0.35
(e0.60 to e0.11)
e0.51
(e0.76 to e0.26)
VE plus EC
40.3
0.26
(e1.28 to 1.80)
e0.83
(e2.27 to 0.61)
e1.08
(e2.52 to 0.36)
NPCS
40.2
0.02
(e0.30 to 0.35)
e0.50
(e0.81 to e0.19)
e0.51
(e0.82 to e0.20)
PC
40.4
0.27
(e0.33 to 0.87)
e0.54
(e1.11 to e0.03)
e0.51
(e1.10 to 0.08)
(95% CI)
b
Model 3
Referent
(95% CI)
Referent
Model 1: year of graduation and sex; model 2: same as model 1, adding maternal age, educational level and residency, single-parent household, maternal smoking, maternal drug abuse, maternal alcohol abuse, and maternal psychiatric diagnosis; model 3: same as previous 2 models, adding small for gestational age, large for gestational age, oligohydramnion, polyhydramnion, maternal diabetes, preeclampsia, head circumference, and gestational age. CI, confidence interval; MOD, mode of delivery; NIVD, noninstrumental vaginal delivery; NPCS, nonplanned cesarean section; PC, planned cesarean section; VE, vacuum extraction; VE plus EC, vacuum extraction and subsequent cesarean section. Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
These differences, which were very similar for vacuum extraction and nonplanned cesarean, cannot be expected to have anything but a minimal impact on the life course of these individuals. Furthermore, our results suggest that vacuum extraction and nonplanned cesarean section are equivalent alternatives for terminating deliveries with respect to cognitive outcomes. No previous studies have shown an association between vacuum extraction delivery and various adverse long-term health outcomes.5-8 One large populationbased study comparable with ours found no effects of mode of delivery on intelligence scores among children at 17 years of age.15 Considering that the observed differences in our study were small, we
believe that these 2 studies could be interpreted in a similar vein. Thus, our results suggest that vacuum extraction is quite a safe method of delivery with respect to cognitive outcomes. It should be noted that this study was conducted in a country with a relatively high rate of vacuum extraction from an international perspective, and therefore, most operators have a high level of experience. It has been shown that a lack of operator experience is related to adverse neonatal outcomes in vacuum extractions.16,17 Our results can therefore not automatically be generalized to settings in which vacuum extraction is a rare choice for terminating a delivery. A major strength of this study is its nationwide population-based design
along with the possibility of acquiring information on confounders through different registers. Information on exposure, outcomes, and potential confounders was collected independently and without involving the study subjects, thus minimizing various types of bias (eg, selection, recall). We excluded 12,523 children from the study because they had not graduated from compulsory school. No indication arose in separate analyses of this group that the exclusion biased our results. Although many potential perinatal confounders were present in the register, many of these have to be considered low-precision proxies for the underlying risk factors, such as asphyxia, thus
TABLE 4
Linear regression for mean grade point average in relation to mode of delivery Model 1 MOD
Mean
b
NIVD
223.8
Referent
Model 2 (95% CI)
b
Model 3 (95% CI)
Referent
b
(95% CI)
Referent
VE
224.3
2.12
(1.23e3.01)
e0.77
(e1.59 to 0.04)
e1.05
(e1.87 to e0.23)
VE plus EC
222.9
1.03
(e4.24 to 6.29)
e3.96
(e8.75 to 0.83)
e4.30
(e9.10 to 0.49)
NPCS
223.1
0.73
(e0.39 to 1.84)
e1.47
(e2.50 to e0.45)
e1.20
(e2.24 to e0.16)
PC
225.4
2.08
(0.01e4.15)
e1.43
(e3.33 to 0.47)
e0.90
(e2.85 to 1.05)
Model 1: year of graduation and sex; model 2: same as model 1, adding maternal age, educational level and residency, single-parent household, maternal smoking, maternal drug abuse, maternal alcohol abuse, and maternal psychiatric diagnosis; model 3: same as models 1 and 2, adding small for gestational age, large for gestational age, oligohydramnion, polyhydramnion, maternal diabetes, preeclampsia, head circumference, and gestational age. CI, confidence interval; MOD, mode of delivery; NIVD, noninstrumental vaginal delivery; NPCS, nonplanned cesarean section; PC, planned cesarean section; VE, vacuum extraction; VE plus EC, vacuum extraction and subsequent cesarean section. Ahlberg. Mode of delivery and cognitive function. Am J Obstet Gynecol 2014.
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making residual perinatal confounding an important concern in the interpretation of our results.
Conclusion Both delivery by vacuum extraction and delivery by nonplanned cesarean section are associated with a marginally lower school performance at 16 years of age, compared with noninstrumental vaginal delivery. The differences, however, are so small that it probably has no impact or only a minimal impact on the life course of a child. This study indicates that delivery by vacuum extraction is quite safe for children from a long-term perspective. REFERENCES 1. Miksovsky P, Watson WJ. Obstetric vacuum extraction: state of the art in the new millennium. Obstet Gynecol Surv 2001;56: 736-51. 2. Edozien LC. Towards safe practice in instrumental vaginal delivery. Best Pract Res Clin Obstet Gynaecol 2007;21:639-55.
www.AJOG.org 3. Simonson C, Barlow P, Dehennin N, et al. Neonatal complications of vacuum-assisted delivery. Obstet Gynecol 2007;109:626-33. 4. Doumouchtsis SK, Arulkumaran S. Head injuries after instrumental vaginal deliveries. Curr Opin Obstet Gynecol 2006;18:129-34. 5. Wen SW, Liu S, Kramer MS, et al. Comparison of maternal and infant outcomes between vacuum extraction and forceps deliveries. Am J Epidemiol 2001;153:103-7. 6. Ngan HY, Miu P, Ko L, Ma HK. Long-term neurological sequelae following vacuum extractor delivery. Aust N Z J Obstet Gynaecol 1990;30:111-4. 7. Blennow G, Svenningsen NW, Gustafson B, Sunden B, Cronquist S. Neonatal and prospective follow-up study of infants delivered by vacuum extraction (VE). Acta Obstet Gynecol Scand 1977;56:189-94. 8. Johanson RB, Heycock E, Carter J, Sultan AH, Walklate K, Jones PW. Maternal and child health after assisted vaginal delivery: fiveyear follow up of a randomised controlled study comparing forceps and ventouse. Br J Obstet Gynaecol 1999;106:544-9. 9. Carmody F, Grant A, Mutch L, Vacca A, Chalmers I. Follow up of babies delivered in a randomized controlled comparison of vacuum extraction and forceps delivery. Acta Obstet Gynecol Scand 1986;65:763-6.
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10. Cnattingius S, Ericson A, Gunnarskog J, Kallen B. A quality study of a medical birth registry. Scand J Soc Med 1990;18:143-8. 11. Marsal K, Persson PH, Larsen T, Lilja H, Selbing A, Sultan B. Intrauterine growth curves based on ultrasonically estimated foetal weights. Acta Paediatr 1996;85:843-8. 12. World Health Organisation. International classification of disorders, 9th ed. Geneva (Switzerland): World Health Organisation; 1986. 13. Swedish National Agency for Education web site. Available at: http://www.skolverket.se/ statistik-och-utvardering/statistik/grundskola/ betyg/betyg-i-grundskolan-lasar-2010-11-1. 160176. Accessed Aug. 30, 2013. 14. Cohen JA. power primer. Psychol Bull 1992;112:155-9. 15. Seidman DS, Laor A, Gale R, Stevenson DK, Mashiach S, Danon YL. Long-term effects of vacuum and forceps deliveries. Lancet 1991;337:1583-5. 16. Murphy DJ, Liebling RE, Patel R, Verity L, Swingler R. Cohort study of operative delivery in the second stage of labour and standard of obstetric care. BJOG 2003;110:610-5. 17. Cheong YC, Abdullahi H, Lashen H, Fairlie FM. Can formal education and training improve the outcome of instrumental delivery? Eur J Obstet Gynecol Reprod Biol 2004;113: 139-44.
