533: The effect of partial compliance on the prevention of recurrent preterm birth in women receiving weekly 17 alpha-hydroxyprogesterone caproate injections

Abstract

To analyze the effect of partial compliance on the prevention of preterm birth (PTB; defined as less than 37 weeks of gestation) among women with previous preterm births and receiving 17 alpha-hydroxyprogesterone caproate (17-P). This is a secondary analysis of a multicenter trial for the prevention of recurrent PTB. Women with a history of PTB were enrolled between 16 and 20 weeks and randomly assigned to weekly injections of either 17-P or placebo. Noncompliance was defined by a gap of at least 10 days between any two injections. Women with 100% compliance rate were compared to those with a compliance rate between 40-80%. Cases with missing data were excluded. The rate of recurrent PTB was the primary outcome. Relative risks were calculated and adjusted to race and the number of previous PTBs. Student's t, Chi-square and mantel-haenszel tests were used as appropriate. A total of 409 women were studied: 370 were 100% compliant, whereas 35 had a compliance rate of 40-80%. The average compliance rate (%) in the group with partial compliance was 62 ± 13. The average gestational age at delivery in the full compliance group was 36w0d ± 4.7 weeks; whereas women with partial compliance delivered in average at 34w1d ± 5.7 weeks. In each group, the PTB rate was significantly reduced in pregnancies receiving 17-P compared to placebo [table]. Women on 17-P whether they were 100% or partially (40-80%) compliant had statistically similar PTB rates [table]. Comparing the homogeneity of both relative risks, the rate of recurrent PTB prevention in both groups was not statistically different (p= 0.1). A 17-P injection compliance rate of 40-80% did not reduce the efficacy of 17-P for the prevention of recurrent preterm birth. This may be explained by the recently reported long half-life of 17-P of 16 days. A randomized trial might help in determining the frequency of injections and the interval between injections of 17-P to prevent recurrent preterm birth. If confirmed, our findings could lead to a dramatic decrease in costs related to prevention of recurrent preterm.