[Maternal underweight and perinatal outcomes: a restrospective cohort study].

Introduction: Some studies have linked maternal underweight with adverse perinatal outcomes such as spontaneous abortion, abruptio placentae, small for gestational age newborn, intrauterine growth retardation and preterm birth. Objective: To determine the influence of maternal underweight in the onset of labor, route of delivery, birth weight, Apgar score and preterm birth. Methods: Retrospective cohort study. We included pregnant women from the Hospital Universitario de Puerto Real. Period of study: 2002-2011. Study group: underweight at the beginning of gestation (BMI < 18.5 kg/m2). Control group: pregnant women with normal body mass index (BMI) at the beginning of gestation (18.5-24.9 kg/m2). The risk (OR) of induction of labor, cesarean section, small for gestational age newborn, macrosomia, 5’ Apgar score < 7, and preterm birth was calculated. Results: The prevalence of underweight was 2.5% versus 58.9% of pregnant women who had a normal BMI. We found no significant differences in the rate of induction of labor, fetal macrosomia, Apgar at 5’ < 7 or preterm delivery. Maternal underweight was associated with a decreased risk of caesarean section (adjusted OR 0.45, 95% CI 0.22 to 0.89) and an increased risk of small for gestational age newborn (adjusted OR 1.74; 95% CI 1.05 to 2.90). Conclusions: Maternal underweight at the start of pregnancy is associated with a lower risk of caesarean section and a greater risk of small for gestational age newborns (birth weight < P10).