- Objective: To investigate whether an abnormal birthweight at term, either small for gestational age (SGA, < 5th centile for gestational age), or large for gestational age (LGA, > 95th centile for gestational age), is a risk factor for perinatal complications as compared with birthweight appropriate for gestational age (AGA). Methods: A population based retrospective cohort analysis of all singleton pregnancies delivered between 1991 and 2014 at Soroka Medical Center. Congenital malformations and multiple pregnancies were excluded. A multivariable generalized estimating equation regression model was used to control for maternal clusters and other confounders. Results: During the study period 228 242 births met the inclusion criteria, of them 91% were AGA (n = 207 652), 4.7% SGA, and 4.3% LGA. SGA significantly increased the risk for perinatal mortality (aOR 5.6, 95%CI 4.5–6.8) and low 5-minute Apgar scores (aOR 2.2, 95%CI 2.0–2.4) while LGA did not. SGA and LGA were both significant risk factors for cesarean delivery. LGA was significantly associated with shoulder dystocia and post-partum hemorrhage (aOR = 13.6, 95%CI 10.9–17.0, and aOR 1.7, 95%CI 1.2–2.6, respectively). Conclusions: Extreme birthweights at term are significantly associated with adverse maternal and neonatal outcomes. As opposed to SGA, LGA is not independently associated with perinatal mortality.