Incidence of respiratory distress syndrome following antenatal betamethasone: role of sex, type of delivery, and prolonged rupture of membranes.

Premature male infants have a higher incidence of respiratory distress syndrome (RDS) than female infants (male/female = 1.7:1.) With the demonstration that antenatal use of betamethasone significantly reduces the incidence of RDS, a proportional reduction or possibly a complete elimination of the discrepancy between the two sexes might be expected. The role that sex, type of delivery, and prolonged rupture of membranes (PROM) may play in the development of RDS was tested in a prospective study of RDS prevention with betamethasone. A full course of betamethasone, ie, 12 mg, 24 hours apart, was given antenatally to 94 infants of 27 to 34 weeks gestation. The incidence of RDS in male infants was 29.1% vs 8.6% in female infants (P less than .02). The incidence of RDS among male babies delivered by cesarean section (30.3%) or vaginally (29.7%) was not statistically different, nor was there a difference between those with PROM greater than 24 hours (26.9%) and those without PROM (31.8%). The same was true of the incidence of RDS among female infants: cesarean section (14.2%) vs vaginal delivery (6.2%) and PROM greater than 24 hours (8%) vs (9.5%) without PROM. We conclude that: (1) Prevention of RDS with betamethasone is far more effective in female infants. The natural ratio of male/female of 1.7:1 becomes 3.4:1. (2) Once lung maturity has been achieved with betamethasone, the type of delivery plays no role in the development of RDS. (3) PROM does not add extra protection from RDS in the 27- to 34-week gestational age range.