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.