The role of vaginal progesterone for preterm birth prevention in women with threatened labor and shortened cervix diagnosed after 24 weeks of pregnancy

Objective: To determine whether vaginal progesterone treatment for women with a short cervix, diagnosed after 24 weeks of pregnancy, reduces preterm birth rates. Methods: A retrospective cohort study that included women with a singleton pregnancy, threatened preterm labor, and a short cervix measured between 24⁺⁰ and 33⁺⁶ weeks. Women who received vaginal progesterone were compared with women who did not receive progesterone. The primary outcome was spontaneous preterm birth before 37 weeks of pregnancy. Results: Patients who received vaginal progesterone had a lower rate of preterm delivery at less than 37 weeks of pregnancy (18.2% [22/121] versus 28.9% [73/253]; adjusted hazard ratio 0.50; 95% confidence interval 0.28–0.73, P = 0.001). The diagnosis-to-delivery interval was significantly greater in patients who received progesterone than in those who did not—median time to delivery in weeks: 8.2 (interquartile range [IQR] 6.2–9.8) versus 6.6 (4.8–8.8), (P < 0.001). The frequency of neonatal intensive care unit admission was significantly lower in patients who received progesterone than in those who did not (8.3% [10/121] versus 16.2% [41/253], P = 0.04). Conclusions: The administration of vaginal progesterone to patients with an episode of threatened premature labor and a short cervix presenting after 24 weeks of pregnancy was associated with lower rates of premature births.