A risk model to predict probability of maternal intrapartum transfers from a free-standing birth centre: 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 (Journal of Clinical Nursing, 2014)