Objective: 1) To examine the impact of maternal pregestational Body Mass Index (BMI) and smoking on infant abdominal circumference (AC) and birth weight. 2) To define reference curves for AC and birth weight in offspring of healthy, non-smoking, normal weight women. Design: Population-based study. Setting: Data from the Danish Medical Birth Registry. Population: All live singletons without congenital malformations in Denmark 2004-2010. Methods: Data on 366,886 singletons at gestational age (GA) 35+0 to 41+6 (weeks+days) were extracted and analysed using linear and multivariate regressions. Main outcome measures: Birth AC and weight in relation to pregestational maternal BMI, maternal smoking and medical conditions (any). Results: Infant AC and birth weight increased significantly (p<0.0001) with increasing maternal BMI. Smoking was negatively associated with AC resulting in a reduction in AC (95% CI) of 0.47 (0.49-0.45) cm and a reduction in birth weight of 173 (177-169) g. In offspring of healthy non-smoking mothers with normal pregestational BMI, mean AC (±2SD) ranged from 30.1 (25.9-34.3) cm at GA 35 weeks to 33.9 (30.1- 37.7) cm at GA 41 weeks (girls), and from 30.2 (25.8-34.6) cm at GA 35 weeks to 34.1 (30.3-37.9) cm at GA 41 weeks (boys). Mean birth weight ranged from 2581 (1831-3332) g at GA 35 weeks to 3705 (2864-4546) g at GA 41 weeks (girls) and from 2666 (1924-3407) g at GA 35 weeks to 3852 (2971-4734) g at GA 41 weeks. Pregestational BMI correlated more to the Z-score of birth weight than to Z-score of AC (p < 0.0001). Conclusion: Birth AC and weight are affected by maternal smoking status and pregestational BMI, and pregestational BMI correlates more to birth weight than to AC. Using data from offspring of healthy, non-smoking mothers with normal pregestational BMI we have provided new normative curves for birth AC and weight.