Antenatal corticosteroid administration is a critical fetal intervention, and the use of a rescue protocol is now standard practice. Rescue antenatal corticosteroid may improve overall accuracy of antenatal corticosteroid administration timing, but this observation and its effect on the initial course is unknown.

We sought to compare the accuracy of antenatal corticosteroid administration before and after the implementation of a rescue antenatal corticosteroid protocol.

We performed a retrospective cohort study of patients who received a minimum of 1 dose of antenatal corticosteroid from 2006-2012 at the University of Washington Medical Center with the use of the University of Washington Medical Center Pharmacy Database. For inclusion, subjects were required to be admitted, receive the initial antenatal corticosteroid course at 24-34 weeks gestation, and deliver at University of Washington Medical Center. We designated 2 groups that were based on when rescue antenatal corticosteroid became standard practice at University of Washington Medical Center: before rescue antenatal corticosteroid (2006-2008) and after rescue antenatal corticosteroid (2009-2012). Primary outcome was delivery within any optimal antenatal corticosteroid window, which was defined as 48 hours to 7 days after the first dose or third dose. We also compared delivery within the optimal window of the initial and rescue antenatal corticosteroid courses independently and assessed antenatal corticosteroid timing by the indication for delivery. Chi squared and independent sample t-tests were used to compare results.

From 2006-2012, 1356 women met inclusion criteria, 601 before and 755 after rescue antenatal corticosteroid. The study groups demonstrated similar demographics, with the exception of more white women in the group after rescue antenatal corticosteroid (47% vs 60%; P < .01) and delivered at comparable gestational ages (32.7 vs 32.6 weeks; P = .59). Availability of a second course did not increase total subjects who delivered within any optimal window (26.5% vs 28.5%; P = .41). Frequency of delivery within the initial course optimal window did not change after the introduction of the rescue course protocol (26.1% vs 26.4%; P = .92). Similarly, of the 73 subjects who received rescue antenatal corticosteroid, 24.7% delivered in the optimal window of the second course. Delivery within the optimal window varied by indication for antenatal corticosteroid, with highest accuracy among maternal indications (41.2% in any optimal window), followed by preterm premature rupture of membranes (32.1%). Lowest administration accuracy was among women with antenatal cervical shortening and advanced cervical dilation; only 2.8% and 6.3% delivered within the optimal window, respectively. Furthermore, for women with antenatal cervical shortening, the mean gestational age of delivery was 35.1 weeks, and the median interval from antenatal corticosteroid administration to delivery was 55 days (interquartile range, 34–72 days).

The opportunity for a second course of antenatal corticosteroid did not improve the number of women who delivered within any optimal antenatal corticosteroid window. Administration timing was similar for the initial course and the rescue course, with approximately one-quarter of women delivering within the optimal antenatal corticosteroid window. These findings likely reflect the few circumstances in which rescue antenatal corticosteroid is useful and the poor predictability of preterm birth. Future focus should be aimed at tools to predict the timing of preterm birth to optimize antenatal corticosteroid administration.