Meconium-stained amniotic fluid is reported in up to 22% of term deliveries, and varying proportions of infants delivered through meconium-stained fluid develop meconium aspiration syndrome, a condition with reported case fatality rates ranging from 5% to 40%. Randomized trials suggest that amnioinfusion of saline is associated with a reduced risk of meconium aspiration syndrome and operative delivery. This international, randomized, controlled study enrolled 2003 women from 13 countries who had thick meconium staining of amniotic fluid during labor and a singleton fetus with a gestational age of 36 weeks or more. A total of 1998 women were randomly assigned to amnioinfusion or standard care after being stratified according to the presence or absence of variable fetal heart rate decelerations. Amnioinfusion was done by infusing 800 mL of sterile saline transcervically over 40 minutes and continuing until a maximum of 1500 mL was delivered.
A total of 1975 women were available for analysis. The study groups were comparable sociodemographically and in baseline obstetric characteristics. More than 90% of women in both groups underwent continuous fetal heart rate monitoring. A composite primary outcome, including perinatal death, moderate or severe meconium aspiration syndrome, or both, occurred in 4.5% of infants in the amnioinfusion group and 3.5% of the control group, for a relative risk (RR) of 1.26 (95% confidence interval [CI], 0.82–1.95). The respective rates of moderate or severe meconium aspiration syndrome were 4.4% and 3.1%, yielding a RR of 1.39 (95% CI, 0.88–2.19). There were 5 perinatal deaths in each group (0.5%). Mild respiratory distress occurred in approximately 3% of each group. Stratified analysis showed no significant effect of amnioinfusion on the frequency of the primary outcome whether or not fetal heart decelerations were present. Rates of oropharyngeal suctioning, laryngoscopy, and intubation in the delivery room were comparable, as were the proportions of infants having meconium below the vocal cords. Fetal heart rate monitoring demonstrated abnormalities that justified clinical intervention in 14.1% of the amnioinfusion group and 13.9% of the control group (RR, 1.02; 95% CI, 0.79–1.30). No significant group differences were found in rates of cesarean delivery, maternal fever in the peripartum period, maternal death, or serious morbidity.
Amnioinfusion for thick meconium staining of amniotic fluid did not lower the risk of perinatal death, moderate or severe meconium aspiration syndrome, or other serious neonatal disorders in this study, and it should not be recommended for this indication when standard peripartum surveillance is assured.