Loss to follow-up in cohort studies may result in biased association estimates. Of 61,895
women entering the Danish National Birth Cohort and completing the first data-collection …

Background The aim of pregnancy cohorts was to understand causes and development of
health and disease throughout the life course. A major challenge in cohort studies is to avoid …

A follow-up questionnaire on maternal health was distributed within the Danish National
Birth Cohort (established in 1996–2002) 14 years after the index birth. Responses were …

Background: Participation rates in large cohort studies have decreased during the last 2
decades. The consequences of this trend for relative risk estimation are unknown. Methods …

BACKGROUND: Prenatal maternal smoking has been associated with attention-
deficit/hyperactivity disorder (ADHD) in children, but the causal nature of this association is …

Introduction: Smoking during pregnancy has been reported to be associated with a twofold
to fourfold increased risk of attention-deficit hyperactivity disorder (ADHD) in the offspring …

Abstract Introduction: The Medical Birth Registry of Norway provides national coverage of all
births in Norway. In this study trends of smoking at the beginning of pregnancy and the …

Background Maternal smoking during pregnancy is an established risk factor for low infant
birth weight, but evidence on critical exposure windows and timing of fetal growth restriction …

Selfselection in epidemiological studies may introduce selection bias and influence the
validity of study results. To evaluate potential bias due to selfselection in a large …

METHODS: The current study used data from the Norwegian Mother and Child Cohort Study
(n> 100 000 children). Mothers and fathers reported on smoking during pregnancy, and …