[1] Midwife Las Higueras Hosp, Obstet & Gynecol Serv, Talcahuano, Chile
[2] Inst Clin Effectiveness & Hlth Policy IECS Argent, Dept Mother & Child Hlth Res, Buenos Aires, DF, Argentina
[3] Univ Concepcion, Med Fac, Dept Med Educ, Concepcion, Chile
[4] Univ Concepcion, Dept Obstet & Puericulture, Med Fac, Casilla 160-C, Concepcion, Chile