702: Is there a racial disparity in the efficacy of progesterone to prevent preterm birth?

Black women are at higher risk than women of other races for preterm birth (PTB) and its recurrence. This study was performed to determine whether there is a racial disparity in the efficacy of progesterone when given to women at high PTB risk. Secondary analysis of a multicenter, randomized, double-blind, placebo-controlled trial of progesterone to prevent PTB, the ProVagGel study. Pregnant women with either a prior spontaneous PTB <35wks or midtrimester short cervix (18-23wks) were randomized to 90mg intravaginal progesterone gel (Prochieve®) or identical placebo given daily from 18-23 wks until 37wks, membrane rupture, or delivery. A secondary analysis after the trial demonstrated a benefit of progesterone in women with midtrimester cervical shortening (≤30mm), defined as the efficacy subpopulation. Key outcome data was stratified and analyzed by maternal race for the entire study cohort and the efficacy subpopulation. 620 women comprised the study population described above. The racial distribution was 26% black, 35% white, 19% Asian/Pacific Islander (A/P), and 20% Hispanic/other (H/O). The rate of PTB ≤32wks was 14% black, 8% white, 7% A/P, and 14% H/O. The overall rate of PTB ≤32wks (11%) was not reduced with progesterone, regardless of race. However, in the efficacy subpopulation (n=116), an improvement in gestational age at delivery with progesterone treatment was noted: 35.2wks (placebo) vs 36.6wks (progesterone), p=0.038. The improvement in gestational age at delivery was more significant in women of black race (n=30) than other races: 34.3wks (placebo) vs 37.6wks (progesterone), p=0.032; differences for other races: white (n=26) p=0.098, A/P (n=32) p=0.599, and H/O (n=28) p=0.429. Prophylactic administration of vaginal progesterone gel is associated with a later gestational age at delivery when given to women at especially high risk of PTB, those with midtrimester cervical shortening and black race. The sample size of the efficacy subpopulation limits conclusions regarding other races.