Effect of vaginal progesterone in tocolytic therapy during preterm labor in twin pregnancies: Secondary analysis of a placebo-controlled randomized trial - Hernandez, Wagner R.; Francisco, Rossana Pulcinelli Vieira; Bittar, Roberto Eduardo; Gomez, Ursula T; Zugaib, Marcelo; Brizot, Maria de Lourdes (Journal of obstetrics and gynaecology research, 2017)