Invited commentary: The use of sibship studies to detect familial confounding.

The authors discuss how the sibship design can be used to detect and control for familial confounding. Family-level confounding is especially problematic when estimating modest individual-level effects in the presence of familial confounders with large effects. This circumstance arises frequently in studies which relate indicators of fetal growth, such as birth weight, to outcomes that are strongly associated with parental socioeconomic status and genes.

Associations of birth size, gestational age, and adult size with intellectual performance: evidence from a cohort of Norwegian men.

The influences of prenatal and postnatal growth on intellectual performance are unclear. We examined the associations of birth size and gestational age with intellectual performance and explored whether these associations were influenced by adult body size and social factors. In this nationwide cohort study, the records of 317,761 male infants registered in the Medical Birth Registry of Norway (1967-1979) were linked to the Norwegian Conscript Service (1984-1999).

Maternal epilepsy and offsprings' adult intelligence: a population-based study from Norway.

Purpose: We examined if children of mothers with epilepsy had normal intelligence, speculating that either epilepsy or its therapy might affect this parameter.

Methods: In a population-based cohort study in Norway, information on maternal epilepsy reported to the Medical Birth Registry of Norway, 1967-1979 was linked to information on 18-19-year-old men's intellectual ability and anthropometric measures ascertained by the Norwegian Conscripts Service, 1984-1999. The standardized intelligence test (IQ score) was reported as single-digit standard scores with values from 1 to 9.

Associations of birth defects with adult intellectual performance, disability and mortality: population-based cohort study.

Infants born with birth defects have poorer outcomes in terms of mortality and disability, but the long-term intellectual outcome in children with birth defects is generally unknown. We assessed the long-term associations of various birth defects with mortality and disability, and evaluated whether high mortality and disability were reflected in impaired intellectual performance at age 18. In this nationwide cohort study, records of 9,186 males with and 384,384 without birth defects, registered in the Medical Birth Registry of Norway (1967-1979) were linked to the National Conscript Service (1984-1999).

Size at birth and gestational age as predictors of adult height and weight.

Background: Both birth length and birth weight are associated with height in adulthood and may have independent contributions to adult body size, but the effects of gestational age on these associations have not been fully evaluated. Our objective was to examine the independent contributions of gestational age, and of length and weight at birth, on adult (age 18 years) height and weight, with a special focus on the effects of being born preterm.

Methods: In this nationwide cohort study, records of 348,706 male infants included in the Medical Birth Registry of Norway (1967-1979) were linked to the Norwegian Conscripts Service (1984-1999).

Breech delivery and intelligence: a population-based study of 8,738 breech infants.

Objective: Long-term intellectual performance in breech-presented infants may be negatively affected by vaginal delivery. We evaluated the effect of presentation at birth and delivery mode on intellectual performance at age 18 years in a nationwide population study.

Methods: We studied 8,738 male infants in breech and 384,832 males in cephalic presentation registered in the Medical Birth Registry of Norway, 1967-1979, and linked to data registered at the National Conscript Service, 1984-1999.