Use of amniocentesis in preterm gestation with ruptured membranes.

Sixty-one patients with preterm rupture of membranes were studied. Transabdominal amniocentesis was performed successfully in 42 patients (68.8%). Among these 42, 26 (61.9%) had a lecithin:sphingomyelin (L:S) ratio of 1.8 or greater and 16 (38.1%) demonstrated pulmonary immaturity. Amniotic fluid obtained from vaginal pooling was compared to fluid obtained transabdominally in seven patients and did not demonstrate any significant differences in L:S values. Gram stain and subsequent culturing of amniotic fluid obtained transabdominally was accomplished in 41 patients. Seven of the 41 patients (17.0%) had bacteria on Gram stain and/or subsequent amniotic fluid growth. All patients with either bacteria on Gram stain or a positive amniotic fluid culture developed clinical amnionitis or endometritis. Review of the neonatal morbidity and mortality in relation to gestational age of infants with preterm rupture of membranes suggests that: 1) In infants at less than 32 weeks' gestation, amniocentesis need not be done for pulmonary maturity as the morbidity of prematurity in this group is too high even in the presence of pulmonary maturity. 2) In infants at 32 to 34 weeks' gestation, amniocentesis for L:S ratio, Gram stain, and culture is helpful in selecting those in whom delivery should be instituted. 3) In infants at greater than 34 weeks' gestation, the neonatal morbidity is sufficiently reduced so that delivery should be considered except in cases of suspected delayed pulmonary maturation.