Preterm birth (PTB) is defined as birth before 37 completed weeks of gestation, which occurs in approximately 10% of all pregnancies [1]. PTB causes about 70% of all neonatal deaths of nonanomalous infants, as well as neonatal morbidities including respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, bronchopulmonary dysplasia and long-term complications such as cerebral palsy [2,3]. The PTB rate has risen worldwide, and in South Korea, the PTB rate has also risen from 4.3% in 1995 to 10% in 2003 [1,4]. There are many known risk factors for PTB, but one of the most ObjectiveTo evaluate whether the administration of vaginal natural micronized progesterone is associated with reduction of recurrent preterm birth (PTB) in women with prior history of spontaneous PTB. MethodsWe retrospectively evaluated the obstetric and neonatal outcomes of all women with history of spontaneous PTB that delivered from January 2008 through April 2012. Spontaneous PTB was defined as PTB before 37 weeks of gestation due to spontaneous preterm labor or preterm premature rupture of membranes. Pregnancies with multiple gestation and those who received cerclage operation during previous or current pregnancy were excluded. Patients in the progesterone group were instructed to selfadminister 100 or 200 mg vaginal micronized natural progesterone capsule. We evaluated the difference in recurrent PTB rate between the progesterone group (n = 73) and the non-user group (n = 158). ResultsThe incidence of recurrent spontaneous PTB before 37 weeks' gestation was significantly lower in the progesterone group than the non-user group (21.9% vs. 43.0%, P=0.002). Multivariate analysis showed that progesterone therapy was associated with a decrease in the incidence of recurrent PTB before 37 weeks' gestation (odds ratio, 0.382; 95% confidence interval, 0.169-0.863; P=0.021) independent of confounding variables. ConclusionMicronized vaginal progesterone supplement therapy was associated with a reduction of recurrent PTB risk in women with previous spontaneous PTB history.

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