ABSTRACT Objective To estimate the risks of maternal and neonatal complications in pregnancies with macrosomia. Methods Thiswasaretrospectivecohortstudyconducted at a large maternity unit in the UK between January 2009 and December 2016. The incidence of maternal and neonatal complications in pregnancies with macrosomia, defined as birth weight (BW) >4000g, and in those with severe macrosomia, defined as BW > 4500 g, was compared with that in pregnancies with normal BW (2500–4000g). Regression analysis was performed to determine odds ratios (ORs) for complications in macrosomic pregnancies compared to those with normal BW. Results The study population of 35548 pregnancies included 4522 (12.7%) with macrosomia, of which 643 (1.8%) had severe macrosomia, and 31 026 (87.3%) with normal BW. In the macrosomia group, the adjusted OR was 3.1 (95% CI, 2.6–3.6) for Cesarean section for failure to progress, 2.4 (95% CI, 2.0 – 3.0) for severe postpartum hemorrhage, 2.3 (95% CI, 1.9–2.8) for obstetric anal sphincter injury, 10.4 (95% CI, 8.6 – 12.6) for shoulder dystocia, 28.5 (95% CI, 8.9 – 90.7) for obstetric brachial plexus injury, 32.3 (95% CI, 3.8–278.2) for birth fractures and 4.4 (95% CI, 2.2–8.8) for hypoxic-ischemic encephalopathy. The respective values in pregnancies with severe macrosomia were 4.3 (95% CI, 3.1 – 6.1), 2.9 (95% CI, 1.9 – 4.4), 3.1 (95% CI, 1.9–5.1), 28.7 (95% CI, 20.8–39.8), 73.9 (95% CI, 15.1–363.2), 87.2 (95% CI, 7.7–985.0) and 13.8 (95% CI, 5.2–36.8). Conclusion Macrosomia is associated with serious adverse perinatal outcomes. This study provides accu- rate estimates of risks to aid in pregnancy management.