The relationship between oligohydramnios and the onset of preterm labor in preterm premature rupture of membranes

Objective: The objective of this study was to determine whether a reduced amniotic fluid volume was associated with the onset of preterm parturition in patients with preterm premature rupture of membranes. Study Design: An amniotic fluid index was determined before transabdominal amniocentesis in 129 patients with preterm premature rupture of membranes (gestational age ≤35 weeks). Amniotic fluid was cultured for aerobic and anaerobic bacteria, as well as for mycoplasmas. Survival techniques were used for analysis. Results: Amniotic fluid index was ≤5 cm in 29% of patients (38/129). Patients with an amniotic fluid index of ≤5 cm had a significantly higher rate of positive amniotic fluid culture than those with an amniotic fluid index of >5 cm (42% [16/38] vs 18% [16/91]; P< .01). Spontaneous preterm delivery within 24 hours and 48 hours was more frequent among patients with an amniotic fluid index of ≤5 cm than those with an amniotic fluid index of >5 cm (for 24 hours, 29% vs 12%; for 48 hours, 42% vs 21%; P< .05 for each). The amniocentesis-to-delivery interval was significantly shorter in patients with an amniotic fluid index of ≤5 cm than in patients with an amniotic fluid index of >5 cm (median, 38 hours; range, 0.2-1310 hours; vs median, 100 hours; range 0.1-2917 hours; P< .01). Moreover, Cox proportional hazards model analysis indicated that an amniotic fluid index of ≤5 cm was a significant predictor of the duration of the pregnancy after adjustment for gestational age and the results of amniotic fluid culture (odds ratio, 2.4; 95% confidence interval, 1.4-3.9; P< .001). Conclusion: Patients with preterm premature rupture of membranes and an amniotic fluid index of ≤5 cm are at increased risk for a shorter interval to delivery. (Am J Obstet Gynecol 2001;184:459-62.)