gestation, and two telephone interviews after birth when the child was approximately 6 and 18 months old. The women included in the cohort were mostly Caucasians as only 4 percent were born outside Scandinavia.
This study used information about 60,892 liveborn, full-term singleton (≥ 37 wk of gestation) infants whose mothers had participated in the first pregnancy and the first postpartum interview and provided information about prepregnancy BMI, GWG and postpartum weight retention 6 months after birth. In the following, the data and methods of the study will be shortly presented. A more detailed description has been published (Nohr et al., 2008).
The main exposures were prepregnancy BMI and GWG. In the first pregnancy interview, the women reported their prepregnancy weight and height, which was used to calculate their prepregnancy BMI and categorize them according to the World’s Health Organization’s definitions as underweight (BMI < 18.5 kg/m2), normal weight (18.5 ≤ BMI < 25 kg/m2), overweight (25 ≤ BMI < 30 kg/m2), and obese (BMI ≥ 30 kg/m2) (WHO, 2000). Gestational weight gain was based on information from the telephone interview 6 months after birth. At this time, the woman was asked “How much (in kg) was your total gain in pregnancy?” Her response was divided into four categories: low (< 10 kg) medium (10-15 kg), high (16-19 kg, and very high (≥ 20 kg). The medium category, which has been associated with minimum infant mortality in other populations (IOM, 1990) was used as reference.
From the first pregnancy interview, we also used information about the mother’s age at conception, parity, smoking, alcohol intake and physical exercise during pregnancy, and social status defined by education and occupation. Information about duration of breastfeeding was reported by the women in the first postpartum interview. The categorization of these variables is described in greater detail elsewhere (Nohr et al., 2008).
Pregnancy outcomes during late pregnancy included preeclampsia/eclampsia, chronic/gestational hypertension and gestational diabetes and were identified through linkage to the National Hospital Discharge Register. Because we suspected some underreporting of gestational diabetes, we added self-reported information about this disease from the pregnancy interviews.
Birth complications were also identified in the National Hospital Discharge Register and included instrumental deliveries, which in nearly all