Isolated oligohydramnios in the term pregnancy: is it a clinical entity?

OBJECTIVE: To test the hypothesis that when isolated oligohydramnios is found at term in the otherwise normal pregnancy, perinatal outcome is worse than pregnancies with normal amniotic fluid volume. METHODS: All obstetric patients at term (37 to 41-67 weeks gestation) who underwent induction of labor for the sole indication of oligohydramnios during the study period were compared to a control group consisting of spontaneously laboring patients with normal amniotic fluid index (API), matched for gestational age and parity. Oligohydramnios was defined as AFI <5.0 cm. Exclusion criteria were: non-cephalic presentation, multiple gestation, ultrasound estimated fetal weight <10th percentile for gestational age, hypertensive complications, diabetes mellitus and ruptured membranes. Outcome variables examined included: meconium-stained amniotic fluid (MSAF), route of delivery, indication for cesarean section (CS), acidosis (arterial cord pH<7.15), low 5-minute Apgar (<7), admission to NICU, and cost of hospitalization for mother and infant. RESULTS: A total of 366 patients met inclusion criteria (oligo groupn=183; control group-n = 183). Maternal characteristics and demographic data were similar between the two groups. AFI < 5.0 nlAFI P valueOR (95% CI) AFI (cm ± S.E.) 3.1 ±0.1 7.6 ±0.2 <0.001 BW (g ±S.E.) 3398 ±34 3427 ±35 NS MSAF (%) All 24.9 23.6 1.1 (0.7-1.8) ModThick 13.7 12.6 1.1 (0.6-2.1) Acidosis (%) 10.4 7.1 1.5 (0.7-3.2) Low Apgar (%) 1.1 0.5 2.0 (0.2-22.4) NICU (%) 16.6 11.5 1.5 (0.8-2.8) CS (%) 15.8 6.6 2.7 (1.3-5.4) Birthweight There was no difference between the two groups in rate of CS for fetal distress [33.3% vs. 23.1%, OR 1.7 (0.4-7.6)]. The study group also had significantly higher cost of maternal hospitalization ($2977 vs. $2510, p<0.01). CONCLUSION: The data in our study suggest that perinatal outcome in patients with isolated oligohydramnios in an otherwise normal term pregnancy is comparable to that of the general population (normal AFI). Thus, clinical intervention (induction of labor) for isolated otigohydramnios will result only in increased CS rate and cost of care for the mother.