Association between borderline amniotic fluid levels and adverse perinatal outcome: systematic review and meta-analysis

Abstract

Objectives: The aim of the present study was to evaluate adverse perinatal outcomes in low-risk singleton pregnancies with borderline oligohydramnios.

Methods: A comprehensive literature search was conducted for observational cohort studies that compared perinatal outcomes in low-risk singleton pregnancies between those with borderline oligohydramnios, defined as an amniotic fluid index (AFI) of 5.1-8.0 cm, and those with a normal AFI. EMBASE, MEDLINE and Web of Science databases were searched for studies published from inception to July 2024. The quality of the studies was assessed using the Newcastle-Ottawa Scale. Meta-analyses were performed using a random-effects model to calculate pooled proportions and 95% CIs for each outcome in both groups. The outcomes assessed included overall Cesarean delivery (CD), CD owing to fetal distress, 5-min Apgar score < 7, low birth weight (LBW), admission to the neonatal intensive care unit (NICU), meconium-stained amniotic fluid, meconium aspiration syndrome, non-reassuring fetal heart rate during labor, operative vaginal delivery and neonatal death.

Results: The search yielded 6902 results, of which eight met the inclusion criteria for the meta-analysis. From these eight studies, 799 singleton pregnancies with borderline oligohydramnios and 1512 singleton pregnancies with normal AFI were analyzed. Analysis revealed an association of borderline oligohydramnios with increased risks of overall CD (odds ratio (OR), 2.20 (95% CI, 1.70-2.84); P < 0.01), CD owing to fetal distress (OR, 2.70 (95% CI, 1.70-4.30); P < 0.01), 5-min Apgar score < 7 (OR, 2.18 (95% CI, 1.38-3.44); P < 0.01), LBW (OR, 2.32 (95% CI, 1.27-4.25); P < 0.01) and NICU admission (OR, 2.63 (95% CI, 1.63-4.24); P < 0.01), compared with normal AFI. A sensitivity analysis that included only term pregnancies revealed significantly higher risks of overall CD, CD owing to fetal distress, LBW and NICU admission in those with borderline oligohydramnios compared to those with normal AFI. Among the pregnancies in which AFI was measured within 1 week before delivery, the risks of overall CD and CD owing to fetal distress were significantly higher.

Conclusions: We report an association of borderline oligohydramnios with adverse perinatal outcomes among low-risk singleton pregnancies. The increased risks of these perinatal outcomes highlight the need for more frequent monitoring in pregnancies with borderline oligohydramnios. Further research is required to understand the potential benefits and risks of early labor induction and to develop specific guidelines for managing borderline oligohydramnios. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Keywords: amniotic fluid index; borderline oligohydramnios; liquor amnii; low‐risk pregnancy; perinatal outcome.