Maternal pre-pregnant body mass index, maternal weight change and offspring birthweight.

Objective: To estimate the association between maternal pre-pregnant body mass index (BMI) and maternal weight change during pregnancy and offspring birthweight using the BMI classification developed by World Health Organization (WHO) and adopted by the Institute of Medicine (IOM) in 2009.

Design: The Norwegian Mother and Child Cohort Study (MoBa) is a population-based pregnancy cohort study conducted by The Norwegian Institute of Public Health.

Setting: Women were recruited from all geographic areas of Norway.