Journal of Obstetrics and Gynaecology, 2014; Early Online: 1–4 © 2014 Informa UK, Ltd. ISSN 0144-3615 print/ISSN 1364-6893 online DOI: 10.3109/01443615.2014.968101
Relationship between pre-pregnancy maternal BMI with spontaneous preterm delivery and birth weight F. Sharifzadeh1, M. Kashanian1, S. Jouhari1 & N. Sheikhansari2 1Department of Obstetrics and Gynecology, Akbarabadi Teaching Hospital, Iran University of Medical Sciences, Tehran, Iran and
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2Student of Public Health, Faculty of Medicine, University of Southampton
The aim of the present study was to find the relationship between pre-pregnancy maternal body mass index (BMI) with spontaneous preterm delivery and birth weight. A prospective cohort study was performed on 576 pregnant women. Maternal BMI was determined at the first prenatal visit between 8–12 weeks’ gestation and considered as the pre-pregnancy maternal weight. The women were then monitored up to delivery. Out of 576 women, 396 completed the study. The demographics of the women in all BMI groups did not differ with regard to age, height, history of abortion and employment. A total of 21 women (5.3%) were underweight; 198 women (50%) were normal weight; 117 women (29.5%) were overweight and 60 (15.2%) were obese. There were no cases of morbidly obese (BMI ⬎ 40 kg/m2) women. Obesity in women had a positive correlation with higher gestational age at the time of delivery (r ⴝ 0.213, p ⴝ 0.015) and a heavier birth weight (r ⴝ 0.361, p ⴝ 0.008). Low birth weight had a correlation with low maternal BMI (r ⴝ 0.157, p ⴝ 0.041). Macrosomia was greater in obese women (p ⴝ 0.022) and BMI had a positive correlation with macrosomia (r ⴝ 0.224, p ⴝ 0.034). Preterm delivery showed a negative correlation with maternal BMI (r ⴝ –0.124, p ⴝ 0.004) and the women with a lower BMI had a greater number of preterm deliveries (p ⴝ 0.035). Keywords: Body mass index (BMI), low birth weight (LBW), macrosomia, obesity, pregnancy outcome, preterm delivery
risk of preterm labour in underweight women, but at the same time, reported more preterm labour due to medical indications in obese women. In contrast, Honest et al. (2005) concluded that pre-pregnancy weight is not helpful in predicting the risk of preterm birth before 37 weeks’ gestation. They stated that further studies should evaluate this subject with greater precision. Schieve et al. (2000) reported a higher risk of preterm labour in the cases of low weight gain during pregnancy, particularly if it was accompanied with low pre-pregnancy weight. Naeye (1990) reported a higher rate of preterm labour and low birth weight and prenatal loss in underweight women, while Sebire et al. (2001a) have reported the protective effect of low maternal weight on the pregnancy outcome. Similarly, Bhattacharya et al. (2007) concluded a better pregnancy outcome in low maternal weight, and that higher BMI is associated with increased incidence of macrosomia, pregnancy-induced hypertension and preeclampsia, as well as cesarean delivery. With respect to different studies with different results, and limited research from Iran on this topic, the purpose of the present study was to evaluate the effect of pre-pregnancy weight on preterm delivery and birth weight irrespective of maternal weight gain during pregnancy. Because BMI is the best index for comparing weight, the women were evaluated in four different BMI categories, and the relationship between different BMI with preterm delivery and birth weight was studied.
Material and methods Introduction Preterm delivery and low birth weight, as well as macrosomia, are among the most serious problems in pregnancy and the consideration of their risk factors, in order to manage them more efficiently, is a matter for serious concern. Pre-pregnancy maternal weight and its effect on birth weight and preterm delivery have been evaluated, as well as maternal weight gain during pregnancy. Low pre-pregnancy weight has been considered as a risk factor for preterm labour and also may have an effect on birth weight, independent of weight gain during pregnancy (Gibbs et al. 2008; Saliha et al. 2009). Borkowski and Mielniczuk (2007) evaluated the relationship between preterm labour and low pre-pregnancy BMI, and reported that both low maternal weight gain and low pre-pregnancy BMI increase the risk of preterm labour. Wise et al. (2010) reported a greater
The study was conducted as a prospective cohort study in Akbarabadi Teaching Hospital, in Tehran, Iran, between March 2008 and March 2009. This is a very busy hospital in the south of Tehran with an average number of deliveries of around 12,000 per year. Written informed consent was obtained from all participants and institutional review board approval and institutional ethics committee approval were given. A total of 390 women was considered sufficient for the sample size in order to obtain a power of 90% (α ⫽ 0.05, 1-β ⫽ 0.085) with a significance level of 5%. Regarding the exclusion criteria during the study, 525 women were monitored up to delivery and 396 women completed the study. Maternal BMI was determined at the first prenatal visit between 8 and12 weeks’ gestation, and it was considered as the pre-pregnancy maternal BMI. All women were then monitored up to delivery.
Correspondence: M. Kashanian, Department of Obstetrics and Gynecology, Akbarabadi Teaching Hospital, No 9, Mostaghimi Alley, Khajeh Nasir Toosi Avenue, 16117, Tehran, Iran. E-mail: [email protected]
2
F. Sharifzadeh et al. Table I. Demographic characteristics of women according to BMI.
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Underweight (n ⫽ 21) Characteristics
n
Maternal age (year) (mean ⫾ SD) Maternal height (cm) (mean ⫾ SD) Maternal weight (kg) (mean ⫾ SD) Gravidity Primigravid Multigravid History of abortion No 1 ⬎1
26.43 ⫾ 3.5 162.7 ⫾ 7.8 47.61 ⫾ 5.8
(%)
9 12
n
(%)
24.91 ⫾ 4.9 157.8 ⫾ 5.8 54.71 ⫾ 6.5
42.9 57.1
21 0 0
Normal weight (n ⫽ 198)
100 0 0
Overweight (n ⫽ 117) n
Obese (n ⫽ 60)
(%)
n
(%)
p value
27.95 ⫾ 5.3 156.5 ⫾ 7.1 66.36 ⫾ 8.7
28.25 ⫾ 6.7 157.8 ⫾ 6.1 83.32 ⫾ 9.3
NS NS 0.003
141 57
71.2 28.8
45 72
38.5 61.5
12 48
20 80
0.02
183 12 3
92.4 6.1 1.5
96 21 0
82.1 17.9 0
54 6 0
90 10 0
NS
NS, not significant.
Inclusion criteria were: singleton pregnancy; maternal age range 18–35; gestational age ⬍ 12 weeks (according to a reliable LMP and ultrasound confirmation); a live fetus and a healthy mother without any history of maternal disease. Exclusion criteria were: gestational age ⬎ 12 weeks; multifetal pregnancy; maternal diabetes or hypertension; maternal anaemia; history of any known systemic disorder or drug use, except usual supplements; smoking; polyhydramnios and oligohydramnios; known uterine malformations according to history and previous sonography; fetal anomalies; known uterine infection; rupture of membrane; any vaginal bleeding during pregnancy and any indications for preterm induction of labour. After determining their BMI, the women were divided according to their BMI into four categories: underweight (BMI ⬍ 18.5 kg/m2); normal weight (BMI 18.6–24.9 kg/m2); overweight (BMI ⫽ 25–29.2 kg/m2) and obese (BMI ⫽ 30–40 kg/m2). These women were then monitored up to delivery. Birth weight and gestational age at the time of delivery were recorded. Low birth weight was defined as birth weight ⬍ 2,500 g, macrosomia was defined as birth weight ⬎ 4,500 g and preterm delivery was defined as delivery at ⬍ 37 weeks. The obtained data were analysed using SPSS 15. Student’s t-test, χ2-test, one-way ANOVA, Pearson’s correlation coefficient, bivariant correlation analysis and linear regression model were used. A p value of ⬍ 0.05 was considered as significant. Student’s t-test was used to compare metric data and the χ2-test was used for comparing the proportions. One-way ANOVA was used to compare means between the groups. Pearson’s correlation coefficients were used to calculate the correlation between paired datasets. Bivariant correlation analysis was performed in order to determine the association between maternal BMI and neonatal birth weight and gestational age. Linear regression model was used to determine the correlation between maternal BMI and neonatal outcome, including birth weight and gestational age at delivery. Overall, 525 women were monitored up to delivery. During the study, 129 women were excluded (PPROM, pregnancy induced
hypertension and pre-eclampsia, vaginal bleeding, fetal anomalies, polyhydramnios, oligohydramnios and lost to follow-up). In total, 396 women completed the study.
Results The mean age of the women was 26.41 ⫾ 5.32 years (range 18–35). The mean height and weight of the women were 157.61 ⫾ 6.5 cm (range 142–175 cm) and 61.9 ⫾ 12.9 kg (range 40–107 kg), respectively. The mean BMI of the women was 24.9 ⫾ 4.7 kg/ m2 (range 17–39). A total of 390 (98.5%) women were housewives, three (0.75%) were teachers and three (0.75%) were workers. Of the women, 207 (52.3%) were primipara and 189 (47.7%) were multipara. A total of 354 (89.45%) of the women did not have any history of spontaneous abortion; 39 (9.8%) had a history of one abortion and three (0.75%) had a history of more than one abortion. The women in all BMI groups did not differ according to age, height, history of abortion and employment. Table I shows the demographic characteristics of women according to their BMI: 21 of the 396 women (5.3%) were underweight; 198 (50%) were normal weight; 117 (29.5%) were overweight and 60 (15.2%) were obese. There were no cases of morbidly obese (BMI ⬎ 40 kg/m2). Maternal age did not show any significant difference between the four groups (Table I) but there was a significant difference between the four groups for gravidity. There was no difference between the groups with regard to a history of abortion (Table I). Table II compares the pregnancy outcome in the four groups. The mean gestational age at the time of delivery and mean birth weight were 37.8 ⫾ 2.8 weeks and 2,961.6 ⫾ 689.1 g, respectively. In total, 75 neonates (18.9%) had a birth weight ⬍ 2,500 g and nine (2.3%) were macrosomic (⬎ 4,500 g). Preterm delivery (delivery at ⬍ 37 weeks) occurred in 24 (6.1%) women. Obese women had the highest rate of macrosomia in the four groups (10%), however, there were more instances of low birth weight (15%) in obese women (Table II).
Table II. Pregnancy outcome according to BMI. Underweight (n ⫽ 21) Characteristics Gestational age (weeks) (mean ⫾ SD) Birth weight (g) (mean ⫾ SD) Birth weight ⬍ 2,500 g Macrosomia Preterm delivery
n
(%)
36.3 ⫾ 1.5 2,808.2 ⫾ 647.6 18 85.71 0 0 9 42.85
Normal weight (n ⫽ 198) n
(%)
36.9 ⫾ 2.3 2,923.6 ⫾ 594.1 27 13.63 1 0.5 6 3
Overweight (n ⫽ 117) n
(%)
37.6 ⫾ 1.8 3,025.6 ⫾ 741.5 21 17.9 2 1.7 6 5.1
Obese (n ⫽ 60) n
(%)
37.9 ⫾ 1.2 3,264.6 ⫾ 584.9 9 15 6 10 3 5
Relationship between pre-pregnancy maternal BMI with spontaneous preterm delivery and birth weight 3 One-way ANOVA showed a significant difference in the four groups according to birth weight. Obesity was correlated positively with higher gestational age at delivery (r ⫽ 0.213, p ⫽ 0.015) and more birth weight (r ⫽ 0.361, p ⫽ 0.008). Low maternal BMI correlated with low birth weight (r ⫽ 0.157, p ⫽ 0.041). Prevalence of macrosomia was significantly higher in obese women (p ⫽ 0.022). BMI had a positive correlation with macrosomia (r ⫽ 0.224, p ⫽ 0.034). Preterm delivery had a negative correlation with maternal BMI (r ⫽ –0.124, p ⫽ 0.004) and underweight women had a greater number of spontaneous preterm deliveries (p ⫽ 0.035).
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Discussion In the present study, low maternal BMI was associated with more spontaneous preterm deliveries and lower birth weight, and in contrast, higher maternal BMI was associated with a higher birth weight and macrosomia. It seems that both high and low maternal BMI have adverse effects on pregnancy outcome (Sahu et al. 2007). Therefore, pre-conception counselling should include maternal BMI as an important risk factor for adverse pregnancy outcome. Wise et al. (2010) reported that low maternal weight was associated with higher preterm labour, which is in agreement with the present study. Khashan and Kenny (2009) showed a higher risk of macrosomia and caesarean delivery, and a lower risk of preterm labour in obese women. However, Rosenberg et al. (2003) reported a correlation between gestational age at delivery and preterm labour with maternal BMI on Chinese women, although a very low maternal BMI showed a significant risk for low birth weight. Therefore it seems that different studies of different ethnic groups should be performed in order to find the real correlation between maternal BMI and pregnancy outcome. Sebire et al. (2001b), in a study on obese women in the UK, showed an increased risk of macrosomia and lower risk of preterm labour before 32 weeks of pregnancy in higher maternal BMI. Lower weight gain during pregnancy for obese women may reduce the risk of macrosomia (Cedergren 2006, 2007; Nohr et al. 2008). A higher risk of preterm delivery due to premature rupture of membranes has been reported in overweight women (Nohr et al. 2007). Cnattingius et al. (1998) showed a lower risk of SGA, but a higher risk of very preterm labour and fetal death in nulliparas who were overweight pre-pregnancy. Regarding the higher risk of fetal death, Reddy et al. (2010) concluded that the evidence for this subject is poor. On the other hand, low pre-pregnancy weight along with low weight gain during pregnancy may increase the rate of preterm labour (Siega- Riz et al. 1996) and low birth weight (Ehrenberg et al. 2003; Doherty et al. 2006). Also it has been reported (Hendler et al. 2005) that obesity prior to pregnancy, may reduce the risk of preterm labour. Correction and controlling of pregnancy weight gain in both underweight and overweight women may control and improve pregnancy outcome (Crane et al. 2009; Oken et al. 2009). An important limitation of the present study is the fact that it was performed irrespective of maternal weight gain during pregnancy; therefore the effects of maternal weight gain on pregnancy outcome cannot be studied. Also, it was performed in a single hospital with a small sample size. Therefore, the results might be generalisable just to Tehran and Iran. However, the clinical implications of the study findings show a need for normalisation of maternal BMI in order to improve pregnancy outcome, and this concept should be considered in pre-conception counselling.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
References Bhattacharya S, Campbell DM, Liston WA, Bhattacharya S. 2007. Effect of body mass index on pregnancy outcome in nulliparous women delivering singleton babies. BMC Public Health 7:168. Borkowski W, Mielniczuk H. 2007. Preterm delivery in relation to combined pregnancy weight gain and prepregnancy body mass. Przeglad Epidemiologiczny 6:577–584. Cedergren MI. 2006. Effects of gestational weight gain and body mass index on obstetric outcome in Sweden. International Journal of Gynaecology and Obstetrics 9:269–274. Cedergren MI. 2007. Optimal gestational weight gain for body mass index categories. Obstetrics and Gynecology 1:359–364. Cnattingius S, Bergstrom R, Lipworth L, Kramer MS. 1998. Prepregnancy weight and the risk of adverse pregnancy outcome. New England Journal of Medicine 338:147–152. Crane JM, White J, Murphy P, Burrage L, Hutchens D. 2009. The effect of gestational weight gain by body mass index on maternal and neonatal outcomes. Journal of Obstetrics and Gynaecology Canada 3:28–35. Doherty DA, Magann EF, Francis J, Morrison JC, Newnham JP. 2006. Pre-pregnancy body mass index and pregnancy outcome. International Journal of Gynecology and Obstetrics 9:242–247. Ehrenberg HM, Dierker L, Milluzzi C, Mercer BM. 2003. Low maternal weight, failure to thrive in pregnancy, and adverse pregnancy outcomes. American Journal of Obstetrics and Gynecology 1:1726–1730. Gibbs RS, Karlan BY, Haney AF, Nygaard I, editors. 2008. Danforth’s obstetrics and gynecology. 10th ed. Philadelphia: Lippincott Williams and Wilkins. p 171. Hendler I, Goldenberg RL, Mercer BM, Imas JD, Meis PJ, Moavad AH. 2005. The preterm prediction study: association between maternal body mass index and spontaneous and indicated preterm birth. American Journal of Obstetrics and Gynecology 1:882–886. Honest H, Bachmann LM, Ngai C, Gupta JK, Kleijnen J, Khan KS. 2005. The accuracy of maternal anthropometry measurements as predictors for spontaneous preterm birth a systematic review. European Journal of Obstetrics, Gynecology, and Reproductive Biology 1:11–20. Khashan AS, Kenny LC. 2009. The effects of maternal body mass index on pregnancy outcome. European Journal of Epidemiology 2: 697–705. Naeye RL. 1990. Maternal body weight and pregnancy outcome. American Journal of Clinical Nutrition 5:273–279. Nohr EA, Bech BH, Vaeth M, Rasmussen KM, Henriksen TB, Olsen J. 2007. Obesity, gestational weight gain and preterm birth: a study within the Danish National Birth Cohort. Paediatric and Perinatal Epidemiology 2:5–14. Nohr EA, Vaeth M, Baker JL, Sorensen Tla, Olsen J, Rasmussen KM. 2008. Combined associations of prepregnancy body mass index and gestational weight gain with the outcome of pregnancy. American Journal of Clinical Nutrition 8:1750–1759. Oken E, Kleinman KP, Belfort MB, Hammitt JK, Gillman MW. 2009. Associations of gestational weight gain with short- and long-term maternal and child health outcomes. American Journal of Epidemiology 1:173–180. Reddy UM, Laughon SK, Sun L, Troendle J, Willinger M, Zhang J. 2010. Prepregnancy risk factors for ante partum still birth in the United States. Obstetrics and Gynecology 116:1119–1126. Rosenberg AG, Wang X, Xing H, Chen C, Chen D, Guang W et al. 2003. Low preconception body mass index is associated with birth outcome in a prospective cohort of Chinese women. Journal of Nutrition 1: 3449–3455. Sahu MT, Agarwal A, Das V, Pandey A. 2007. Impact of maternal body mass index on obstetric outcome. Journal of Obstetrics and Gynaecology Research 3:655–659. Saliha HM, Mbah AK, Alio AP, Clayton HB, Lynch O. 2009. Low pre-pregnancy body mass index and risk of medically indicated versus spontaneous preterm singleton birth. European Journal of Obstetrics, Gynecology, and Reproductive Biology 1:119–123. Schieve LA, Cogswell ME, Scanlon KS, Perry E, Ferre C, Blackmore-Prince C et al. 2000. Prepregnancy body mass index and pregnancy weight gain: associations with preterm delivery. The NMIHS Collaborative Study Group. Obstetrics and Gynecology 9:194–200. Sebire NJ, Jolly M, Aarris JP, Regan L, Robinson S. 2001a. Is maternal underweight really a risk factor for adverse pregnancy outcome?
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F. Sharifzadeh et al.
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A population based study in London. British Journal of Obstetrics and Gynaecology 10:61–66. Sebire NJ, Jolly M, Harris JP, Wadsworth J, Joffe M, Beard RW et al. 2001b. Maternal obesity and pregnancy outcome: a study of 287, 213 pregnancies in London. International Journal of Obesity and Related Metabolic Disorders 2:1175–1182.
Siega-Riz AM, Adair LS, Hobel CJ. 1996. Maternal underweight status and inadequate rate of weight gain during the third trimester of pregnancy increases the risk of preterm delivery. Journal of Nutrition 1:146–153. Wise LA, Palmer JR, Heffner LJ, Rosenberg L. 2010. Prepregnancy body size, gestational weight gain, and risk of preterm birth in African-American women. Epidemiology 2:243–252.
Relationship between pre-pregnancy maternal BMI with spontaneous preterm delivery and birth weight F. Sharifzadeh1, M. Kashanian1, S. Jouhari1 & N. Sheikhansari2 1Department of Obstetrics and Gynecology, Akbarabadi Teaching Hospital, Iran University of Medical Sciences, Tehran, Iran and
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2Student of Public Health, Faculty of Medicine, University of Southampton
The aim of the present study was to find the relationship between pre-pregnancy maternal body mass index (BMI) with spontaneous preterm delivery and birth weight. A prospective cohort study was performed on 576 pregnant women. Maternal BMI was determined at the first prenatal visit between 8–12 weeks’ gestation and considered as the pre-pregnancy maternal weight. The women were then monitored up to delivery. Out of 576 women, 396 completed the study. The demographics of the women in all BMI groups did not differ with regard to age, height, history of abortion and employment. A total of 21 women (5.3%) were underweight; 198 women (50%) were normal weight; 117 women (29.5%) were overweight and 60 (15.2%) were obese. There were no cases of morbidly obese (BMI ⬎ 40 kg/m2) women. Obesity in women had a positive correlation with higher gestational age at the time of delivery (r ⴝ 0.213, p ⴝ 0.015) and a heavier birth weight (r ⴝ 0.361, p ⴝ 0.008). Low birth weight had a correlation with low maternal BMI (r ⴝ 0.157, p ⴝ 0.041). Macrosomia was greater in obese women (p ⴝ 0.022) and BMI had a positive correlation with macrosomia (r ⴝ 0.224, p ⴝ 0.034). Preterm delivery showed a negative correlation with maternal BMI (r ⴝ –0.124, p ⴝ 0.004) and the women with a lower BMI had a greater number of preterm deliveries (p ⴝ 0.035). Keywords: Body mass index (BMI), low birth weight (LBW), macrosomia, obesity, pregnancy outcome, preterm delivery
risk of preterm labour in underweight women, but at the same time, reported more preterm labour due to medical indications in obese women. In contrast, Honest et al. (2005) concluded that pre-pregnancy weight is not helpful in predicting the risk of preterm birth before 37 weeks’ gestation. They stated that further studies should evaluate this subject with greater precision. Schieve et al. (2000) reported a higher risk of preterm labour in the cases of low weight gain during pregnancy, particularly if it was accompanied with low pre-pregnancy weight. Naeye (1990) reported a higher rate of preterm labour and low birth weight and prenatal loss in underweight women, while Sebire et al. (2001a) have reported the protective effect of low maternal weight on the pregnancy outcome. Similarly, Bhattacharya et al. (2007) concluded a better pregnancy outcome in low maternal weight, and that higher BMI is associated with increased incidence of macrosomia, pregnancy-induced hypertension and preeclampsia, as well as cesarean delivery. With respect to different studies with different results, and limited research from Iran on this topic, the purpose of the present study was to evaluate the effect of pre-pregnancy weight on preterm delivery and birth weight irrespective of maternal weight gain during pregnancy. Because BMI is the best index for comparing weight, the women were evaluated in four different BMI categories, and the relationship between different BMI with preterm delivery and birth weight was studied.
Material and methods Introduction Preterm delivery and low birth weight, as well as macrosomia, are among the most serious problems in pregnancy and the consideration of their risk factors, in order to manage them more efficiently, is a matter for serious concern. Pre-pregnancy maternal weight and its effect on birth weight and preterm delivery have been evaluated, as well as maternal weight gain during pregnancy. Low pre-pregnancy weight has been considered as a risk factor for preterm labour and also may have an effect on birth weight, independent of weight gain during pregnancy (Gibbs et al. 2008; Saliha et al. 2009). Borkowski and Mielniczuk (2007) evaluated the relationship between preterm labour and low pre-pregnancy BMI, and reported that both low maternal weight gain and low pre-pregnancy BMI increase the risk of preterm labour. Wise et al. (2010) reported a greater
The study was conducted as a prospective cohort study in Akbarabadi Teaching Hospital, in Tehran, Iran, between March 2008 and March 2009. This is a very busy hospital in the south of Tehran with an average number of deliveries of around 12,000 per year. Written informed consent was obtained from all participants and institutional review board approval and institutional ethics committee approval were given. A total of 390 women was considered sufficient for the sample size in order to obtain a power of 90% (α ⫽ 0.05, 1-β ⫽ 0.085) with a significance level of 5%. Regarding the exclusion criteria during the study, 525 women were monitored up to delivery and 396 women completed the study. Maternal BMI was determined at the first prenatal visit between 8 and12 weeks’ gestation, and it was considered as the pre-pregnancy maternal BMI. All women were then monitored up to delivery.
Correspondence: M. Kashanian, Department of Obstetrics and Gynecology, Akbarabadi Teaching Hospital, No 9, Mostaghimi Alley, Khajeh Nasir Toosi Avenue, 16117, Tehran, Iran. E-mail: [email protected]
2
F. Sharifzadeh et al. Table I. Demographic characteristics of women according to BMI.
J Obstet Gynaecol Downloaded from informahealthcare.com by Memorial University of Newfoundland on 11/27/14 For personal use only.
Underweight (n ⫽ 21) Characteristics
n
Maternal age (year) (mean ⫾ SD) Maternal height (cm) (mean ⫾ SD) Maternal weight (kg) (mean ⫾ SD) Gravidity Primigravid Multigravid History of abortion No 1 ⬎1
26.43 ⫾ 3.5 162.7 ⫾ 7.8 47.61 ⫾ 5.8
(%)
9 12
n
(%)
24.91 ⫾ 4.9 157.8 ⫾ 5.8 54.71 ⫾ 6.5
42.9 57.1
21 0 0
Normal weight (n ⫽ 198)
100 0 0
Overweight (n ⫽ 117) n
Obese (n ⫽ 60)
(%)
n
(%)
p value
27.95 ⫾ 5.3 156.5 ⫾ 7.1 66.36 ⫾ 8.7
28.25 ⫾ 6.7 157.8 ⫾ 6.1 83.32 ⫾ 9.3
NS NS 0.003
141 57
71.2 28.8
45 72
38.5 61.5
12 48
20 80
0.02
183 12 3
92.4 6.1 1.5
96 21 0
82.1 17.9 0
54 6 0
90 10 0
NS
NS, not significant.
Inclusion criteria were: singleton pregnancy; maternal age range 18–35; gestational age ⬍ 12 weeks (according to a reliable LMP and ultrasound confirmation); a live fetus and a healthy mother without any history of maternal disease. Exclusion criteria were: gestational age ⬎ 12 weeks; multifetal pregnancy; maternal diabetes or hypertension; maternal anaemia; history of any known systemic disorder or drug use, except usual supplements; smoking; polyhydramnios and oligohydramnios; known uterine malformations according to history and previous sonography; fetal anomalies; known uterine infection; rupture of membrane; any vaginal bleeding during pregnancy and any indications for preterm induction of labour. After determining their BMI, the women were divided according to their BMI into four categories: underweight (BMI ⬍ 18.5 kg/m2); normal weight (BMI 18.6–24.9 kg/m2); overweight (BMI ⫽ 25–29.2 kg/m2) and obese (BMI ⫽ 30–40 kg/m2). These women were then monitored up to delivery. Birth weight and gestational age at the time of delivery were recorded. Low birth weight was defined as birth weight ⬍ 2,500 g, macrosomia was defined as birth weight ⬎ 4,500 g and preterm delivery was defined as delivery at ⬍ 37 weeks. The obtained data were analysed using SPSS 15. Student’s t-test, χ2-test, one-way ANOVA, Pearson’s correlation coefficient, bivariant correlation analysis and linear regression model were used. A p value of ⬍ 0.05 was considered as significant. Student’s t-test was used to compare metric data and the χ2-test was used for comparing the proportions. One-way ANOVA was used to compare means between the groups. Pearson’s correlation coefficients were used to calculate the correlation between paired datasets. Bivariant correlation analysis was performed in order to determine the association between maternal BMI and neonatal birth weight and gestational age. Linear regression model was used to determine the correlation between maternal BMI and neonatal outcome, including birth weight and gestational age at delivery. Overall, 525 women were monitored up to delivery. During the study, 129 women were excluded (PPROM, pregnancy induced
hypertension and pre-eclampsia, vaginal bleeding, fetal anomalies, polyhydramnios, oligohydramnios and lost to follow-up). In total, 396 women completed the study.
Results The mean age of the women was 26.41 ⫾ 5.32 years (range 18–35). The mean height and weight of the women were 157.61 ⫾ 6.5 cm (range 142–175 cm) and 61.9 ⫾ 12.9 kg (range 40–107 kg), respectively. The mean BMI of the women was 24.9 ⫾ 4.7 kg/ m2 (range 17–39). A total of 390 (98.5%) women were housewives, three (0.75%) were teachers and three (0.75%) were workers. Of the women, 207 (52.3%) were primipara and 189 (47.7%) were multipara. A total of 354 (89.45%) of the women did not have any history of spontaneous abortion; 39 (9.8%) had a history of one abortion and three (0.75%) had a history of more than one abortion. The women in all BMI groups did not differ according to age, height, history of abortion and employment. Table I shows the demographic characteristics of women according to their BMI: 21 of the 396 women (5.3%) were underweight; 198 (50%) were normal weight; 117 (29.5%) were overweight and 60 (15.2%) were obese. There were no cases of morbidly obese (BMI ⬎ 40 kg/m2). Maternal age did not show any significant difference between the four groups (Table I) but there was a significant difference between the four groups for gravidity. There was no difference between the groups with regard to a history of abortion (Table I). Table II compares the pregnancy outcome in the four groups. The mean gestational age at the time of delivery and mean birth weight were 37.8 ⫾ 2.8 weeks and 2,961.6 ⫾ 689.1 g, respectively. In total, 75 neonates (18.9%) had a birth weight ⬍ 2,500 g and nine (2.3%) were macrosomic (⬎ 4,500 g). Preterm delivery (delivery at ⬍ 37 weeks) occurred in 24 (6.1%) women. Obese women had the highest rate of macrosomia in the four groups (10%), however, there were more instances of low birth weight (15%) in obese women (Table II).
Table II. Pregnancy outcome according to BMI. Underweight (n ⫽ 21) Characteristics Gestational age (weeks) (mean ⫾ SD) Birth weight (g) (mean ⫾ SD) Birth weight ⬍ 2,500 g Macrosomia Preterm delivery
n
(%)
36.3 ⫾ 1.5 2,808.2 ⫾ 647.6 18 85.71 0 0 9 42.85
Normal weight (n ⫽ 198) n
(%)
36.9 ⫾ 2.3 2,923.6 ⫾ 594.1 27 13.63 1 0.5 6 3
Overweight (n ⫽ 117) n
(%)
37.6 ⫾ 1.8 3,025.6 ⫾ 741.5 21 17.9 2 1.7 6 5.1
Obese (n ⫽ 60) n
(%)
37.9 ⫾ 1.2 3,264.6 ⫾ 584.9 9 15 6 10 3 5
Relationship between pre-pregnancy maternal BMI with spontaneous preterm delivery and birth weight 3 One-way ANOVA showed a significant difference in the four groups according to birth weight. Obesity was correlated positively with higher gestational age at delivery (r ⫽ 0.213, p ⫽ 0.015) and more birth weight (r ⫽ 0.361, p ⫽ 0.008). Low maternal BMI correlated with low birth weight (r ⫽ 0.157, p ⫽ 0.041). Prevalence of macrosomia was significantly higher in obese women (p ⫽ 0.022). BMI had a positive correlation with macrosomia (r ⫽ 0.224, p ⫽ 0.034). Preterm delivery had a negative correlation with maternal BMI (r ⫽ –0.124, p ⫽ 0.004) and underweight women had a greater number of spontaneous preterm deliveries (p ⫽ 0.035).
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Discussion In the present study, low maternal BMI was associated with more spontaneous preterm deliveries and lower birth weight, and in contrast, higher maternal BMI was associated with a higher birth weight and macrosomia. It seems that both high and low maternal BMI have adverse effects on pregnancy outcome (Sahu et al. 2007). Therefore, pre-conception counselling should include maternal BMI as an important risk factor for adverse pregnancy outcome. Wise et al. (2010) reported that low maternal weight was associated with higher preterm labour, which is in agreement with the present study. Khashan and Kenny (2009) showed a higher risk of macrosomia and caesarean delivery, and a lower risk of preterm labour in obese women. However, Rosenberg et al. (2003) reported a correlation between gestational age at delivery and preterm labour with maternal BMI on Chinese women, although a very low maternal BMI showed a significant risk for low birth weight. Therefore it seems that different studies of different ethnic groups should be performed in order to find the real correlation between maternal BMI and pregnancy outcome. Sebire et al. (2001b), in a study on obese women in the UK, showed an increased risk of macrosomia and lower risk of preterm labour before 32 weeks of pregnancy in higher maternal BMI. Lower weight gain during pregnancy for obese women may reduce the risk of macrosomia (Cedergren 2006, 2007; Nohr et al. 2008). A higher risk of preterm delivery due to premature rupture of membranes has been reported in overweight women (Nohr et al. 2007). Cnattingius et al. (1998) showed a lower risk of SGA, but a higher risk of very preterm labour and fetal death in nulliparas who were overweight pre-pregnancy. Regarding the higher risk of fetal death, Reddy et al. (2010) concluded that the evidence for this subject is poor. On the other hand, low pre-pregnancy weight along with low weight gain during pregnancy may increase the rate of preterm labour (Siega- Riz et al. 1996) and low birth weight (Ehrenberg et al. 2003; Doherty et al. 2006). Also it has been reported (Hendler et al. 2005) that obesity prior to pregnancy, may reduce the risk of preterm labour. Correction and controlling of pregnancy weight gain in both underweight and overweight women may control and improve pregnancy outcome (Crane et al. 2009; Oken et al. 2009). An important limitation of the present study is the fact that it was performed irrespective of maternal weight gain during pregnancy; therefore the effects of maternal weight gain on pregnancy outcome cannot be studied. Also, it was performed in a single hospital with a small sample size. Therefore, the results might be generalisable just to Tehran and Iran. However, the clinical implications of the study findings show a need for normalisation of maternal BMI in order to improve pregnancy outcome, and this concept should be considered in pre-conception counselling.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
References Bhattacharya S, Campbell DM, Liston WA, Bhattacharya S. 2007. Effect of body mass index on pregnancy outcome in nulliparous women delivering singleton babies. BMC Public Health 7:168. Borkowski W, Mielniczuk H. 2007. Preterm delivery in relation to combined pregnancy weight gain and prepregnancy body mass. Przeglad Epidemiologiczny 6:577–584. Cedergren MI. 2006. Effects of gestational weight gain and body mass index on obstetric outcome in Sweden. International Journal of Gynaecology and Obstetrics 9:269–274. Cedergren MI. 2007. Optimal gestational weight gain for body mass index categories. Obstetrics and Gynecology 1:359–364. Cnattingius S, Bergstrom R, Lipworth L, Kramer MS. 1998. Prepregnancy weight and the risk of adverse pregnancy outcome. New England Journal of Medicine 338:147–152. Crane JM, White J, Murphy P, Burrage L, Hutchens D. 2009. The effect of gestational weight gain by body mass index on maternal and neonatal outcomes. Journal of Obstetrics and Gynaecology Canada 3:28–35. Doherty DA, Magann EF, Francis J, Morrison JC, Newnham JP. 2006. Pre-pregnancy body mass index and pregnancy outcome. International Journal of Gynecology and Obstetrics 9:242–247. Ehrenberg HM, Dierker L, Milluzzi C, Mercer BM. 2003. Low maternal weight, failure to thrive in pregnancy, and adverse pregnancy outcomes. American Journal of Obstetrics and Gynecology 1:1726–1730. Gibbs RS, Karlan BY, Haney AF, Nygaard I, editors. 2008. Danforth’s obstetrics and gynecology. 10th ed. Philadelphia: Lippincott Williams and Wilkins. p 171. Hendler I, Goldenberg RL, Mercer BM, Imas JD, Meis PJ, Moavad AH. 2005. The preterm prediction study: association between maternal body mass index and spontaneous and indicated preterm birth. American Journal of Obstetrics and Gynecology 1:882–886. Honest H, Bachmann LM, Ngai C, Gupta JK, Kleijnen J, Khan KS. 2005. The accuracy of maternal anthropometry measurements as predictors for spontaneous preterm birth a systematic review. European Journal of Obstetrics, Gynecology, and Reproductive Biology 1:11–20. Khashan AS, Kenny LC. 2009. The effects of maternal body mass index on pregnancy outcome. European Journal of Epidemiology 2: 697–705. Naeye RL. 1990. Maternal body weight and pregnancy outcome. American Journal of Clinical Nutrition 5:273–279. Nohr EA, Bech BH, Vaeth M, Rasmussen KM, Henriksen TB, Olsen J. 2007. Obesity, gestational weight gain and preterm birth: a study within the Danish National Birth Cohort. Paediatric and Perinatal Epidemiology 2:5–14. Nohr EA, Vaeth M, Baker JL, Sorensen Tla, Olsen J, Rasmussen KM. 2008. Combined associations of prepregnancy body mass index and gestational weight gain with the outcome of pregnancy. American Journal of Clinical Nutrition 8:1750–1759. Oken E, Kleinman KP, Belfort MB, Hammitt JK, Gillman MW. 2009. Associations of gestational weight gain with short- and long-term maternal and child health outcomes. American Journal of Epidemiology 1:173–180. Reddy UM, Laughon SK, Sun L, Troendle J, Willinger M, Zhang J. 2010. Prepregnancy risk factors for ante partum still birth in the United States. Obstetrics and Gynecology 116:1119–1126. Rosenberg AG, Wang X, Xing H, Chen C, Chen D, Guang W et al. 2003. Low preconception body mass index is associated with birth outcome in a prospective cohort of Chinese women. Journal of Nutrition 1: 3449–3455. Sahu MT, Agarwal A, Das V, Pandey A. 2007. Impact of maternal body mass index on obstetric outcome. Journal of Obstetrics and Gynaecology Research 3:655–659. Saliha HM, Mbah AK, Alio AP, Clayton HB, Lynch O. 2009. Low pre-pregnancy body mass index and risk of medically indicated versus spontaneous preterm singleton birth. European Journal of Obstetrics, Gynecology, and Reproductive Biology 1:119–123. Schieve LA, Cogswell ME, Scanlon KS, Perry E, Ferre C, Blackmore-Prince C et al. 2000. Prepregnancy body mass index and pregnancy weight gain: associations with preterm delivery. The NMIHS Collaborative Study Group. Obstetrics and Gynecology 9:194–200. Sebire NJ, Jolly M, Aarris JP, Regan L, Robinson S. 2001a. Is maternal underweight really a risk factor for adverse pregnancy outcome?
4
F. Sharifzadeh et al.
J Obstet Gynaecol Downloaded from informahealthcare.com by Memorial University of Newfoundland on 11/27/14 For personal use only.
A population based study in London. British Journal of Obstetrics and Gynaecology 10:61–66. Sebire NJ, Jolly M, Harris JP, Wadsworth J, Joffe M, Beard RW et al. 2001b. Maternal obesity and pregnancy outcome: a study of 287, 213 pregnancies in London. International Journal of Obesity and Related Metabolic Disorders 2:1175–1182.
Siega-Riz AM, Adair LS, Hobel CJ. 1996. Maternal underweight status and inadequate rate of weight gain during the third trimester of pregnancy increases the risk of preterm delivery. Journal of Nutrition 1:146–153. Wise LA, Palmer JR, Heffner LJ, Rosenberg L. 2010. Prepregnancy body size, gestational weight gain, and risk of preterm birth in African-American women. Epidemiology 2:243–252.
