The use of vaginal progesterone as a maintenance therapy in women with arrested preterm labor: a double-blind placebo-randomized controlled trial.

Background: The efficacy of maintenance tocolytic therapy after successful arrest of preterm labor remains controversial. The purpose of this study was to evaluate the efficacy of 400 mg of daily vaginal progesterone (cyclogest) after successful parenteral tocolysis to increase latency period and improvement of neonatal outcomes in women with threatened preterm labor.
Materials and Methods: In this randomized, double-blind, placebo-controlled trial, 85 participants were randomly allocated to either 400 mg daily of vaginal progesterone ( n  = 45) or placebo ( n  = 40) until 34 weeks of gestation. The primary outcomes were the time until delivery (latency period) and cervical length after 1 week of treatment. Secondary outcome were GA on delivery, type of delivery, incidence of low birth weight, perinatal morbidity and mortality.
Results: Longer mean latency until delivery (53.6 ± 16.8 versus 34.5 ± 12.9) days p  = .0001; longer mean of gestational age on delivery (37.5 ± 2.2 versus 34.2 ± 2.1) weeks p  = .0001; cervical length after 1 week of treatment (27.5 ± 5.5 versus 20.7 ± 3.1) mm p  = .0001; low birth weight 12 (29.3%) versus 19 (57.6%) p  = .01; and NICU admission 9 (22%) versus 15 (45.5%), were significantly different between the two groups. No significant differences were found between neonatal death 1 (2.4%) versus 2 (6.1%), p  = .43; RDS 5 (12.2%) versus 8 (24.2%), p  = .17; and need to mechanical ventilator 2 (5.4%) versus 6 (18.2%) p  = .136, for the progesterone and placebo groups, respectively.
Conclusion: Daily administration of 400 mg vaginal progesterone after successful parenteral tocolysis may increase latency preceding delivery and improves cervical shortening and neonatal outcome in women with preterm labor. Further confirmatory studies are warranted.