Maternal Cigarette Smoking during Pregnancy and Offspring Externalizing Behavioral Problems: A Propensity Score Matching Analysis

A body of empirical research has revealed that prenatal exposure to tobacco smoke is related to a host of negative outcomes, including reduced cognitive abilities, later-life health problems, and childhood behavioral problems. While these findings are often interpreted as evidence of the causal role that prenatal exposure to tobacco smoke has on human phenotypes, emerging evidence has suggested that the association between prenatal exposure to tobacco smoke and behavioral phenotypes may be spurious. The current analysis of data from the Early Childhood Longitudinal Study, Birth Cohort (ECLS-B) revealed that the association between prenatal exposure to cigarette smoke and externalizing behavioral problems was fully accounted for by confounding factors. The implications that these findings have for policy and research are discussed

Academic performance of opposite-sex and same-sex twins in adolescence:A Danish national cohort study

Testosterone is an important hormone in the sexual differentiation of the brain, contributing to differences in cognitive abilities between males and females. For instance, studies in clinical populations such as females with congenital adrenal hyperplasia (CAH) who are exposed to high levels of androgens in utero support arguments for prenatal testosterone effects on characteristics such as visuospatial cognition and behaviour. The comparison of opposite-sex (OS) and same-sex (SS) twin pairs can be used to help establish the role of prenatal testosterone. However, although some twin studies confirm a masculinizing effect of a male co-twin regarding for instance perception and cognition it remains unclear whether intra-uterine hormone transfer exists in humans. Our aim was to test the potential influences of testosterone on academic performance in OS twins. We compared ninth-grade test scores and teacher ratings of OS (n = 1812) and SS (n = 4054) twins as well as of twins and singletons (n = 13,900) in mathematics, physics/chemistry, Danish, and English. We found that males had significantly higher test scores in mathematics than females (.06–.15 SD), whereas females performed better in Danish (.33–.49 SD), English (.20 SD), and neatness (.45–.64 SD). However, we did not find that OS females performed better in mathematics than SS and singleton females, nor did they perform worse either in Danish or English. Scores for OS and SS males were similar in all topics. In conclusion, this study did not provide evidence for a masculinization of female twins with male co-twins with regard to academic performance in adolescence

Being Opposite: Is there Advantage for Social Competence and Friendships in Being an Opposite Sex Twin?

A recent large-scale study of Finnish adolescent twins (Pulkkinen et. al, 2003) reported that individuals from opposite sex twin pairs were more socially adaptive than either individuals from same sex pairs or singletons. This finding raises questions about the social learning effects of being an opposite sex twin. The current paper hypothesised on the basis of this finding, and evidence from singleton populations, that having an opposite sex sibling would yield social advantage. It sought to examine the social competencies of opposite sex pairs and compare them with same sex twins and singletons. The study focused on the preschool years (age 3-6), a period in which the majority of children encounter their first large group, non-familial social experiences. The study obtained reports from parents and teachers of children aged 3-6 years: 72 children (36 pairs) who were dizygotic opposite sex twins (DZOS), 50 children (25 pairs) who were dizygotic same sex twins (DZSS), and 85 singletons of the same age and sex as the twins, who had at least one sibling. Reports were made using standardised measures of social competencies, behaviour problems, language development and friendships. The main effects found were of differences in social competency between twins and singletons. Twins had lower social competency scores. No differences between same sex and opposite sex twins were found. The findings did not support the hypothesis of social advantage for opposite sex twins in early childhood