Is betamethasone effective longer than 7 days after treatment?

OBJECTIVE: To determine whether perinatal outcomes are influenced by the interval between antenatal betamethasone administration and delivery.
METHODS: We did a retrospective cohort analysis of live-born singleton neonates born between 28 and 34 weeks' gestation after a single course of betamethasone, defined as two 12-mg doses over 24 hours. Subjects were grouped according to length of interval between initial betamethasone dose and delivery (1-2 days, 3-7 days, and 8-14 days). We excluded women who had membranes ruptured for longer than 24 hours before delivery, delivery before the second dose of betamethasone, or more than two doses of betamethasone. Data were analyzed by Student t test, chi(2) test, or Fisher exact test. Multiple logistic regression analyses were done using suspected risk factors for respiratory distress syndrome (RDS) and intraventricular hemorrhage (IVH). We calculated that a sample of 200 women would provide more than 80% power to detect a 50% reduction in incidence of RDS for a two-sided test of significance at a critical level of.05.
RESULTS: Among 216 women, 97 delivered in 1-2 days, 78 in 3-7 days, and 41 in 8-14 days after a single course of betamethasone. Groups were similar in selected demographics, tocolytic exposure, gestational age at delivery, modes of delivery, and mean birth weights. There were no significant differences in frequencies of RDS (39.2%, 41.1%, and 36.6%, respectively) or grades 3-4 IVH (1.1%, 1.3%, and 0%, respectively) between groups. Frequencies of selected perinatal infectious outcomes also were similar between groups. Multiple logistic regression analyses found no association between RDS or IVH and delivery more than 7 days from betamethasone therapy.
CONCLUSION: There were no differences in perinatal outcomes in pregnancies delivered 8-14 days after antenatal exposure to betamethasone compared with those delivered within 7 days of exposure.