A risk model to predict probability of maternal intrapartum transfers from a freestanding birth center: PROTRIP tool - Silva, Flora Maria Barbosa da; Oliveira, Sonia Maria Junqueira Vasconcellos de; Osava, Ruth Hitomi; Auil, Fernando; Bick, Debra; Latorre, Maria do Rosário Dias de Oliveira (European Congress on Intrapartum Care - ECIC, 2013)