Perinatal outcome and amniotic fluid index in the antepartum and intrapartum periods: A meta-analysis

OBJECTIVE: Our purpose was to perform a mete-analysis of studies on the ris ks of cesarean delivery for fetal distress, 5-minute Apgar score <7, and um bilical arterial pH <7.00 in patients with antepartum or intrapartum amniot ic fluid index >5.0 or <5.0 cm. STUDY DESIGN: Using a MEDLINE search, we reviewed all studies published bet ween 1987 and 1997 that correlated antepartum or intrapartum amniotic fluid index with adverse peripartum outcomes. The inclusion criteria were studie s in English that associated at least one of the selected adverse outcomes with an amniotic fluid index of less than or equal to 5.0 cm versus >5.0 cm . Contingency tables were constructed for each study, and relative risks an d:standard errors of their logs were calculated. Fixed-effects pooled: rela tive risks were calculated for groups of studies that were homogeneous, whe reas random-effects pooled relative risks were calculated for significantly heterogeneous groups of studies. RESULTS: Eighteen reports describing 10,551 patients met our inclusion Crit eria. Fin antepartum amniotic fluid index of less than or equal to 5.0 cm, in comparison with >5.0 cm, is associated with an increased risk of cesarea n delivery for fetal;distress (pooled relative risk, 2.2; 95% confidence in terval, 1.5-3.4) and an Apgar score of <7 at 5 minutes (pooled relative ris k, 5.2; 95% confidence interval, 2.4-11.3). An intrapartum amniotic fluid i ndex of less than or equal to 5.0 cm is also associated with an increased r isk of cesarean delivery for fetal distress (pooled relative risk, 1.7; 95% confidence interval, 1.1-2.6) and an Apgar score <7 at 5 minutes (pooled r elative risk, 1.8, 95% confidence interval, 1.2-2.7). A poor correlation be tween the amniotic fluid index acid neonatal acidosis was noted-in the-only study that examined this end point. More than 23,000 patients are necessar y to demonstrate-that the incidence of umbilical arterial pH <7.00 is 1.5 t imes higher among those with oligohydramnios in labor than among those with adequate amniotic fluid index (alpha = 0.05; beta = 0.2). CONCLUSIONS: An antepartum or intrapartum amniotic fluid index of less than or equal to 5.0 cm is associated with a significantly increased risk of ce sarean delivery for fetal distress and a low Apgar score at 5 minutes. Ther e are few reports linking amniotic fluid index and neonatal acidosis, the o nly objective assessment of fetal well-being. A multicenter Study with suff icient power should be undertaken to demonstrate that a low amniotic fluid index is associated with an umbilical arterial pH <7.00.