Vaginal progesterone for the prevention of preterm birth in twin gestations: a randomized placebo-controlled double-blind study - Brizot, Maria de Lourdes; Hernandez, Wagner Rodrigues; Liao, Adolfo Wenjaw; Bittar, Roberto Eduardo; Francisco, Rossana Pulcineli Vieira; Krebs, Vera Lucia Jornada; Zugaib, Marcelo (American Journal of Obstetrics & Gynecology, 2015)