http://informahealthcare.com/jmf ISSN: 1476-7058 (print), 1476-4954 (electronic) J Matern Fetal Neonatal Med, Early Online: 1–4 ! 2015 Informa UK Ltd. DOI: 10.3109/14767058.2015.1004051

ORIGINAL ARTICLE

Borderline amniotic fluid index and perinatal outcomes in the uncomplicated term pregnancy Soo Ran Choi

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Department of Obstetrics and Gynecology, Inha University Hospital, Inha University College of Medicine, Incheon, South Korea

Abstract

Keywords

Objective: To determine perinatal outcomes in uncomplicated term pregnancies with a borderline amniotic fluid index (AFI). Methods: A retrospective review was conducted of uncomplicated singleton pregnancies at term (437 weeks). Borderline and normal AFI were defined as 5.1  AFI  8.0 cm and 8.1  AFI  24 cm, respectively. Adverse perinatal outcomes, cesarean delivery for nonreassuring fetal heart rate testing, meconium-stained amniotic fluid, a 5-min Apgar score of 57, admission to the neonatal intensive care unit (NICU), and whether the neonate was small for gestational age were compared between the borderline and normal AFI groups. Results: Borderline AFI was not significantly associated with cesarean delivery for non-reassuring fetal heart rate testing (p ¼ 0.513), meconium-stained amniotic fluid (p ¼ 0.641), admission to the NICU (p ¼ 0.368), or a 5-min Apgar score of57 (p ¼ 1.00). However, the number of neonates who were small for gestational age (p ¼ 0.021) and rates of induction of labor (p50.001) were significantly higher in the borderline group. Multiple logistic regression analysis showed that borderline AFI was not associated with cesarean delivery for non-reassuring fetal heart rate testing (odds ratio [OR] ¼ 0.72, 95% confidence interval [CI] 0.27–1.91, p ¼ 0.52). Conclusion: In uncomplicated term pregnancies, a borderline AFI does not increase the risk of adverse perinatal outcomes.

Borderline amniotic fluid index, perinatal outcomes, term pregnancy

Introduction Amniotic fluid volume is one of several parameters used to assess fetal well-being and perinatal outcomes [1]. Although the factors that influence amniotic fluid volume are complex, decreased amniotic fluid frequently reflects chronic uteroplacental insufficiency and fetal oliguria, as a consequence of the redistribution of fetal blood flow away from the kidneys in an anatomically normal fetus [2]. Borderline oligohydramnios was originally defined as an amniotic fluid index (AFI) of 5.1–8.0 cm by Phelan [3], and represents the lower normal AFI region. Furthermore, it has the potential to progress to oligohydramnios, which has been shown to be associated with adverse fetal and neonatal outcomes [4]. Several studies have been conducted on borderline oligohydramnios and perinatal outcomes, but because they used different inclusion criteria, gestational ages, and definitions of borderline oligohydramnios, the results obtained are difficult to compare [5]. In common clinical practice, borderline oligohydramnios in an uncomplicated term pregnancy is usually considered an indication for the induction of labor.

Address for correspondence: Soo Ran Choi, Department of Obstetrics and Gynecology, Inha University Hospital, 7-206, #3 Sinheung-Dong, Jung-Gu, Incheon, South Korea 400-711. Tel: +82-32-890-3501. Fax: +82-32-890-2274. E-mail: [email protected]

History Received 26 November 2014 Revised 29 December 2014 Accepted 31 December 2014 Published online 27 January 2015

The purpose of the present study was to determine the perinatal outcomes in uncomplicated term pregnancies with a borderline AFI.

Methods We retrospectively reviewed the medical records of all women with uncomplicated singleton pregnancies at a gestational age between 37 + 1 weeks and 42 weeks, between January 2010 and December 2011. Pregnancies associated with membrane rupture, diabetes, a chromosomal or fetal anomaly, elective cesarean delivery, breech presentation, pre-eclampsia, and severe systemic maternal disease were excluded. Multiple pregnancies were also excluded. Ultrasound examinations were performed within 7 d of delivery using an Accuvix XQ (Medison, Seoul, Korea), by residents and well-trained technicians. In accordance with the hospital prenatal care protocol, pregnant women were examined to determine fetal biometrics and the amniotic fluid volume using the AFI. The AFI was determined using the four-quadrant amniotic fluid measurement technique [3]. Borderline and normal AFI were defined as 5.1  AFI  8 cm and 8.1  AFI  24 cm, respectively. When pregnant women had borderline oligohydramnios, our management protocol was to closely monitor them every 1–2 weeks, depending on the AFI. If the AFI decreased more

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J Matern Fetal Neonatal Med, Early Online: 1–4

Table 1. Demographic and obstetric characteristics of subjects.

Age (years) GA at delivery (weeks) Primigravida Weight gain (kg) AFI (cm)

5.1  AFI  8 (n ¼ 112)

8.1  AFI  24 (n ¼ 609)

p value

31.5 ± 4.19 39.21 ± 1.07 74 (66.1) 13.41 ± 4.85 6.46 ± 0.87

31.07 ± 4.18 39.43 ± 1 349 (57.3) 13.73 ± 4.87 11.32 ± 1.84

0.315 0.029 0.83 0.522 50.001

Each characteristic was compared with borderline and normal AFI groups. GA, gestational age; AFI, amniotic fluid index.

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Table 2. Perinatal outcomes in subjects with borderline and normal amniotic fluid index.

Induction of labor Meconium-stained AF Cesarean delivery (total) Cesarean delivery for non-reassuring fetal heart rate testing 5- min A/S57 NICU admission Birth weight (g) SGA Cord around neck Use of PropessÕ

5.1  AFI  8 (n ¼ 112)

8.1  AFI  24 (n ¼ 609)

p value

68 (60.7) 18 (16.1) 14 (12.5) 6 (5.4) 2 (1.8) 0 (.0) 3169.7 ± 392.3 6 (5.4) 32 (28.6) 31 (27.7)

167 (27.4) 109 (17.9) 56 (9.2) 27 (4.4) 12 (2.0) 9 (1.5) 3299.4 ± 355.7 10 (1.6) 169 (27.7) 64 (10.5)

50.001 0.641 0.278 0.513 1.000 0.368 0.001 0.026 0.849 50.001

Each perinatal outcome was compared with borderline and normal AFI groups. AF, amniotic fluid, A/S, Apgar score; NICU, neonatal intensive care unit; SGA, small for gestational age, Cord around neck: more than one pass around the neck of fetus.

than previously, we checked the biophysical profile and performed a non-stress test using electronic monitoring, and induced labor in accordance with the results. We examined the perinatal outcomes of women with a borderline AFI (n ¼ 112), and compared them with those of women with a normal AFI (n ¼ 609). Pregnancy outcome information was obtained by reviewing patient records. The adverse perinatal outcomes examined were cesarean delivery for non-reassuring fetal heart rate testing, meconium-stained amniotic fluid, a 5-min Apgar score of 57, admission to the neonatal intensive care unit (NICU), and small for gestational age (SGA) defined as a birth weight at 510th percentile for gestational age. A dinoprostone vaginal pessary (PropessÕ , Controlled Therapeutic Ltd, East Kilbride, UK) was used to induce labor in women with an unfavorable cervix, whereas augmentation of labor with oxytocin was used for women with a favorable cervix. Statistical analysis was performed by using SPSS for Windows, version 19.0 (SPSS Inc. Chicago, IL). Categorical data were analyzed using the chi-square test or Fisher’s exact test, and continuous variables were analyzed using Student’s t-test. Logistic regression analysis was used to assess the odds ratios of adverse perinatal outcomes. Statistical significance was accepted for p values 50.05. The study was approved by the medical center institutional review board.

Results Of the 721 pregnant women who were eligible for data analysis, 112 (18.4%) had a borderline AFI. Tables 1 and 2 present the demographic and obstetric characteristics of the

study population by AFI. Regarding adverse perinatal outcomes, the rate of cesarean delivery for non-reassuring fetal heart rate tracing (p ¼ 0.513), the incidence of meconium-stained amniotic fluid (p ¼ 0.641), the frequency of a 5min Apgar score of57 (p ¼ 1.00), and admission to the NICU (p ¼ 0.368) were not significantly higher in the borderline AFI group. However, mean gestational age at delivery (p ¼ 0.029) and neonatal weight (p ¼ 0.001) were significantly lower and the SGA rate was higher (p ¼ 0.026). Furthermore, women in the borderline group more frequently required induction of labor (p50.001) and cervical ripening for the induction of labor (p50.001). Table 3 shows the association between borderline AFI and perinatal outcomes. Cesarean delivery for a non-reassuring fetal heart rate tracing was not increased in the borderline group (odds ratio [OR] ¼ 1.254, 95% confidence interval [CI] 0.505–3.116, p ¼ 0.626), and meconium-stained amniotic fluid, NICU admission, and a 5-min Apgar score of 57 were not associated with a borderline AFI. However, SGA and induction of labor were three and four times more common in the borderline group, respectively (OR ¼ 3.391, 95% CI 1.207–9.526, p ¼ 0.021 and OR ¼ 4.09, 95% CI 2.69– 6.219, p50.001, respectively), and dinoprostone vaginal pessary administration for cervical ripening was more frequent in the borderline group (OR ¼ 3.259, 95% CI 2.0–5.311, p50.001). Multiple logistic regression analysis, controlled for nulliparity, induction of labor, SGA, weight gain, and cord around neck (more than one pass around the neck) revealed no significant relationship between a borderline AFI and cesarean delivery for non-reassuring fetal heart rate testing (OR ¼ 0.72, 95% CI 0.27–1.91, p ¼ 0.52).

Perinatal outcomes in borderline amniotic fluid index

DOI: 10.3109/14767058.2015.1004051

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Table 3. The logistic regression analysis of perinatal outcomes.

Induction of labor Use of PropessÕ Meconium-stained AF Cesarean delivery for non-reassuring fetal heart rate testing Birth weight SGA 5- min A/S 57 NICU admission

OR

95% CI

p value

4.09 3.259 0.878 1.254 0.999 3.391 1.052 0

2.69–6.219 2–5.311 0.509–1.515 0.505–3.116 0.998–1 1.207–9.526 0.841–1.315 0

50.001 50.001 0.641 0.626 0.001 0.021 0.658 0.999

The association was showed between borderline AFI and perinatal outcomes. OR, odds ratio; CI, confidence interval; AF, amniotic fluid; SGA, small for gestational age; A/S, Apgar score; NICU, neonatal intensive care unit.

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Discussion This study shows that a borderline AFI in uncomplicated term pregnancies is not associated with adverse perinatal outcomes, that is, with cesarean delivery for non-reassuring fetal heart rate testing, meconium-stained amniotic fluid, admission to NICU, or a 5-min Apgar score 57, but that the rate of labor induction was greater with a borderline AFI. A previous study compared the adverse pregnancy outcomes in subjects with borderline AFI (5.1–8.0 cm) and normal AFI (8.1–25 cm) [6], but reported a significantly higher incidence of cesarean delivery for fetal distress, and higher rates of SGA, 5-min Apgar scores 57, and respiratory distress syndrome (RDS) in the borderline AFI group. We believe that these differences were due to dissimilar ranges of gestational age, and longer times from borderline oligohydramnios identification to delivery. In this previous study, women were enrolled within 2 weeks of delivery during the third trimester, whereas in the present study, women were between 37 + 1 and 42 weeks, and within 1 week of delivery. Interestingly, in another study, low-normal AFI (5–8 cm) was found to be associated with a 16.2% risk of oligohydramnios in the following 4 d, whereas a normal AFI (48 cm) was associated with a 2.3% risk [7]. Baron et al. found no difference between borderline AFI (5.1–8.0 cm) and normal AFI (8.1–20 cm) groups in terms of rates of cesarean delivery for fetal distress, birth weight 52500 g, 5-min Apgar score 57, meconium staining, or admission to a NICU [8]. However, they studied pregnancies of gestational age 426 weeks, included subjects with diabetes and ruptured membrane cases, and did not comment on the time between AFI determination and delivery. Two studies compared groups with borderline AFI (5.1– 10.0 cm) and normal AFI (10–24 cm). Intrauterine growth restriction (IUGR), meconium staining, and intrapartum fetal distress rates were significantly higher in their borderline AFI group [9,10]. Unfortunately, cesarean delivery for nonreassuring fetal heart rate testing and the time between AFI determination and delivery were not investigated, and third trimester pregnancies were included. Oligohydramnios (AFI55 cm) outcome results in two studies were similar to those of the borderline group in the present study. In uncomplicated pregnancies at term, oligohydramnios did not affect the rate of operative delivery for abnormal fetal heart rate testing, and the incidence of labor induction was increased compared with a normal amniotic fluid volume (AFI45 cm) [11,12].

The prediction of fetal well-being based on AFI is not straightforward. In a recent review, it was not recommended that obstetric practice regarding the commencement of antepartum testing or delivery be modified in pregnant women with a borderline AFI without another obstetric indication [5]. The present study supports this view, because borderline oligohydramnios in an uncomplicated term pregnancy was not found to be associated with any adverse perinatal outcomes except SGA, low birth weight, and the induction of labor. The other technique used to measure amniotic fluid volume is the single deepest vertical pocket method. One meta-analysis concluded that this technique should be considered the method of choice for the assessment of amniotic fluid volume [13]. Furthermore, when AFI was used for fetal surveillance, a lack of assurance of fetal well-being led to increased oligohydramnios diagnosis, labor induction, and cesarean delivery rates [13]. In conclusion, borderline oligohydramnios in an uncomplicated term pregnancy was not found to be a risk factor for adverse perinatal outcomes. However, this study is limited by its retrospective design and relatively small cohort. We suggest a larger-scale randomized controlled clinical trial be conducted to determine the perinatal outcomes in borderline oligohydramnios, and to compare the merits of the AFI and the deepest vertical pocket method.

Declaration of interest This work was supported by Inha University Hospital Research Grant. The author has no potential conflict of interest to declare.

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Borderline amniotic fluid index and perinatal outcomes in the uncomplicated term pregnancy.

To determine perinatal outcomes in uncomplicated term pregnancies with a borderline amniotic fluid index (AFI)...
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