The effect of intramuscular progesterone on the rate of cervical shortening

The purpose of the study was to evaluate whether 17-alpha-hydroxyprogesterone caproate (17-OHPC) exposure is associated with the rate of cervical shortening.

Women with a history of spontaneous preterm delivery (PTD) at <37 weeks' gestation who had serial cervical length measurements (2009-2012) were identified. 17-OHPC administration and outcome data were collected. We excluded patients with multiple gestations, indicated PTDs, major fetal anomalies, cerclage, and vaginal progesterone use. The rate of cervical shortening was modeled in relation to 17-OHPC status with the use of methods for longitudinal data analysis.

Two hundred thirty-seven patients with 1171 cervical length measurements were included, of whom 184 patients (77.6%) were exposed to 17-OHPC. Gestational age, number of previous PTDs, gestational age at initiation, and interval between cervical length examinations were similar between the 2 groups, although women who were not exposed to 17-OHPC were more likely to have delivered multiples in their previous PTD (24.5% vs 4.4%; P < .01). In the entire cohort, the rate of cervical shortening was identical, regardless of 17-OHPC exposure (0.85 mm per week). Among term deliveries, the rates of cervical shortening per week, on average, were 0.9 and 0.8 mm per week among women with and without 17-OHPC, respectively (P = .76). Among preterm deliveries, the corresponding rates were 0.8 and 1.2 mm, respectively, among women with and without 17-OHPC (P = .67).

Cervical shortening among women with previous preterm delivery occurs at a similar rate, regardless of exposure to 17-OHPC.