Gestational diabetes and pre-pregnancy overweight: Possible factors involved in newborn macrosomia Pablo Roberto Olmos 1,5 , Gisella Rosa Borzone 2 , Roberto Ignacio Olmos 1 , Claudio Nicolás Valencia 1 , Felipe Andrés Bravo 1 , María Isabel Hodgson 3 , Cristián Gastón Belmar 4 , José Andrés Poblete 4 , Manuel Orlando Escalona 1 and Bernardita Gómez 1 Departments of 1 Nutrition, Diabetes and Metabolism and 2 Respiratory Diseases and 3 Pediatrics and 4 Obstetrics and Gynecology, College of Medicine, and 5 Department of Electrical Engineering, College of Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile Abstract Aim: Good glycemic control in gestational diabetes mellitus (GDM) seems not to be enough to prevent macrosomia (large-for-gestational-age newborns). In GDM pregnancies we studied the effects of glycemic control (as glycosylated hemoglobin [HbA1c]), pre-pregnancy body mass index (PP-BMI) and gestational weight gain per week (GWG-W) on the frequency of macrosomia. Methods: We studied 251 GDM pregnancies, divided into two groups: PP-BMI < 25.0 kg/m 2 (the non- overweight group; n = 125), and PP-BMI  25.0 kg/m 2 (the overweight group; n = 126). A newborn weight Z-score > 1.28 was considered large-for-gestational-age. Statistical analysis was carried out using the Student’s t-test and c 2 -test, receiver–operator characteristic curves and linear and binary logistic regressions. Results: Prevalence of macrosomia was 14.9% among GDM (n = 202/251, 88.4%) with good glycemic control (mean HbA1c < 6.0%), and 28.1% in those with mean HbA1c  6.0% (n = 49/251, P < 0.025). Macrosomia rates were 10.4% in the non-overweight group and 24.6% in the overweight group (P = 0.00308), notwithstanding both having similar mean HbA1c (5.48  0.065 and 5.65  0.079%, P = 0.269), and similar GWG-W (0.292  0.017 and 0.240  0.021 kg/week, P = 0.077). Binary logistic regressions showed that PP-BMI (P = 0.012) and mean HbA1c (P = 0.048), but not GWG-W (P = 0.477), explained macrosomia. Conclusions: Good glycemic control in GDM patients was not enough to reduce macrosomia to acceptable limits (<10% of newborns). PP-BMI and mean HbA1c (but not GWG-W) were significant predictors of macrosomia. Thus, without ceasing in our efforts to improve glycemic control during GDM pregnancies, patients with overweight/obesity need to be treated prior to becoming pregnant. Key words: diabetes, gestational, macrosomia, obesity, overweight. Introduction There is a worldwide consensus that delivery of a mac- rosomic or large-for-gestational-age (LGA) infant is associated with increased frequencies of prolonged labor, operative delivery, shoulder dystocia and bra- chial plexus trauma. 1 In the particular case of the mac- rosomia that is due to gestational diabetes mellitus (GDM), maternal hyperglycemia – and its conse- quence, fetal hyperinsulinemia – are positively corre- lated to neonatal excess body mass. 2 However, tight glucose control seems not to be enough to prevent macrosomia in GDM, as other variables have emer- ged as independent factors of excessive fetal growth, Received: October 21 2010. Accepted: May 6 2011. Reprint request to: Dr Pablo R. Olmos, Department of Nutrition, Diabetes and Metabolism, College of Medicine, Pontificia Universidad Católica de Chile, Alameda 340, Santiago 6513492, Chile. Email: polmos@med.puc.cl doi:10.1111/j.1447-0756.2011.01681.x J. Obstet. Gynaecol. Res. Vol. 38, No. 1: 208–214, January 2012 208 © 2011 The Authors Journal of Obstetrics and Gynaecology Research © 2011 Japan Society of Obstetrics and Gynecology