Vaginal progesterone and the risk of preterm birth in patients with short cervix beyond 24 weeks

The efficacy of vaginal progesterone (VP) in preventing spontaneous preterm birth (sPTB) among women with a mid-trimester short cervix is well established. However, data regarding prevention of sPTB using VP beyond 24 weeks are limited and inconclusive. The aim of the present study was to evaluate the association of VP on the risk of sPTB in women diagnosed with a cervical length (CL) <25 mm beyond 24 weeks.

This retrospective cohort study included women with singleton pregnancies, no history of prior PTB and CL <25 mm diagnosed between 24⁺⁰-33⁺⁶ weeks. The primary outcomes were rates of sPTB at <37, <34, <32 and <28 weeks.

Among 890 eligible women, 490 received VP, and 400 did not. Women in the VP group were diagnosed earlier (29.5 ± 2.8 vs. 31.4 ± 2.4 weeks, P < 0.001) and had shorter CL (17.5 ± 5.3 vs. 19.8 ± 5 mm, P < 0.001). Logistic regression and 1:1 matched analysis, adjusted for gestational age at diagnosis and CL, showed no significant effect of VP on the risk of sPTB at <37, <34, <32, or <28 weeks. The mean interval from diagnosis to delivery was similar between groups (48.6 ± 24.0 vs. 49.5 ± 24.6 days, P = 0.57). Subgroup analysis showed no benefit of VP in asymptomatic women or those with arrested preterm labor.

In women with a singleton pregnancy, no history of prior PTB and a short cervix diagnosed after 24 weeks, VP was not associated with reduced sPTB risk or prolonged pregnancy duration.