Preterm prelabor amniorrhexis: outcome of live births

To investigate the risk of postnatal death in pregnancies with preterm prelabor amniorrhexis in relation to gestational age at both amniorrhexis and delivery.

In 172 singleton pregnancies with preterm prelabor amniorrhexis resulting in live births, postnatal survival and cause of death were examined in relation to gestational age at both amniorrhexis and delivery. In 108 of the patients, the amniotic fluid index (AFI) and fetal breathing movements were determined, and in 98, the internal thoracic circumference and cardiothoracic ratio were also measured. The value of these indices in the prediction of pulmonary hypoplasia was examined.

There were 30 (17%) deaths, 18 of which were due to pulmonary hypoplasia and 12 to prematurity-related complications. Survival was related to both gestational age at amniorrhexis (50% for amniorrhexis before 20 weeks' gestation and 98% when amniorrhexis occurred after 25 weeks) and gestational age at delivery (57% for those born at 24-28 weeks' gestation and 96% for those born after 32 weeks). Pulmonary hypoplasia was also related to both gestational age at amniorrhexis (causing 92% of deaths in the group with amniorrhexis at less than 20 weeks' gestation but none of those with amniorrhexis after 23 weeks) and gestational age at delivery (causing 50% of deaths in the group delivered at 24-28 weeks' gestation and 87% of deaths in infants delivered after 28 weeks). Fetal breathing movements were present in 33 and 63% of cases with and without pulmonary hypoplasia, respectively. The corresponding values for internal thoracic circumference below the 2.5 percentile were 33 and 9%, respectively. There were no significant differences in the AFI or cardiothoracic ratio between the cases with and without pulmonary hypoplasia. Multivariate analysis demonstrated that the only characteristic that contributed significantly in distinguishing between cases with and without pulmonary hypoplasia was gestational age at amniorrhexis.

In pregnancies with preterm prelabor amniorrhexis, postnatal survival is related to both gestational age at amniorrhexis and gestational age at delivery. Prediction of pulmonary hypoplasia is primarily dependent on gestational age at amniorrhexis.