maintenance therapy by vaginal progesterone after threatened idiopathic preterm labor: a randomized placebo-controlled double-blind trial

background: patients with arrested preterm labor (ptl) are at increased risk for recurrence of preterm birth (ptb). maintenance tocolysis after arrest of acute ptl is of questionable value. the objective of this study was to evaluate the efficacy of 200 mg vaginal progesterone in order to prevent ptb in women with episodes of threatened ptl. materials and methods: this is a randomized double blind clinical trial study.women with singleton pregnancies between 28-36 weeks of gestation, who were hospitalized for ptl were included. a total of 173 pregnant patients were randomly allocated to receive 200 mg vaginal progesterone suppositories (n=86) or placebo (n=87) daily until the 36th gestational week. the two groups were compared relative to demographic characteristics, incidence of ptb before 34 and 37 weeks, and maternal and neonatal complications. data were analyzed by chi-square and fisher’s exact tests. results: mean latency until delivery in the cases was longer than the control group (23.88 ± 18.01 vs. 16.67 ± 12.9; p=0.004).treatment with progesterone was not associated with a reduction in the rate of ptb before 34 weeks [cases: 9 (10.8%) vs. controls: 8 (10%)] and 37 weeks [cases: 45 (54.2%) vs. controls: 33 (41.2%)]. log rank analysis revealed a significant difference for mean time to delivery between the two groups (p=0.028). there were no significant differences for neonatal and maternal complications in the two groups. conclusion: prophylactic administration of 200 mg vaginal progesterone suppositories after successful tocolysis in patients with threatened idiopathic ptl is associated with a longer latency to delivery, but failed to reduce the rate of ptb (registeration number: irct138706051096n1).