Vaginal progesterone and risk of preterm birth in asymptomatic women with short cervix diagnosed after 24 weeks of gestation

Background: The optimal management of asymptomatic women with a short cervix first identified after 24 weeks of gestation remains uncertain. Although vaginal progesterone is effective for preventing preterm birth when cervical shortening is detected in the mid-trimester, its role in women with incidentally detected late cervical shortening is unclear. Objective: To evaluate whether vaginal progesterone treatment is associated with a reduced risk of spontaneous preterm birth among asymptomatic women with a short cervix first identified after 24 weeks of gestation. Study Design: This retrospective cohort study included asymptomatic singleton pregnancies with a cervical length of 25 mm or less first identified between 24+0 and 33+6 weeks of gestation. Patients were categorized according to whether vaginal progesterone therapy was initiated following the diagnosis of a short cervix or whether expectant management was chosen. The primary outcome was spontaneous preterm birth before 37 weeks of gestation. Secondary outcomes included spontaneous preterm birth before 34, 32, and 28 weeks, diagnosis-to-delivery interval, and selected maternal and neonatal outcomes. Time-to-delivery analyses were performed using Kaplan–Meier estimates and univariable Cox proportional hazards regression. Results: Among 154 asymptomatic women included in the analysis, 65 (42.2%) received vaginal progesterone and 89 (57.8%) were managed expectantly. Spontaneous preterm birth before 37 weeks occurred in 16 women (24.6%) in the progesterone group and in 17 women (19.1%) in the expectant management group (P=.41). Rates of spontaneous preterm birth before 34 weeks were similarly low in both groups (3.1% vs 5.6%, P=.46). Kaplan–Meier analysis demonstrated no difference in time to delivery between groups (log-rank P=.60). In Cox proportional hazards regression, vaginal progesterone treatment was not associated with time to delivery (HR: 1.28; 95% confidence interval, 0.65–2.54; P=.47). Women treated with progesterone had a shorter cervical length at diagnosis and a higher rate of previous preterm birth compared with those managed expectantly (17.5±5.2 vs. 20.8±4.2 mm, P<.001). Multivariable logistic regression analysis similarly demonstrated no independent association between vaginal progesterone treatment and preterm birth (aOR: 0.89, 95% CI, 0.38–2.13). Maternal and neonatal outcomes were similar between the groups. These findings remained consistent across time-to-event analysis and multivariable adjustment for baseline differences. Conclusions: In asymptomatic women with a short cervix first identified after 24 weeks of gestation, vaginal progesterone therapy was not associated with a reduction in spontaneous preterm birth.