Testing the fetal origins hypothesis in twins: the Birmingham twin study

Aims/hypothesis. To test whether the link between birthsize and raised bloo d pressure or glucose tolerance is due to genetic or intrauterine factors, we studied whether differences in birthweight between pairs of monozygous a nd dizygous twins are associated with adult differences in blood pressure a nd glucose tolerance. Methods. A sample of 58 monozygous and 140 dizygous twins were identified f rom a register of births in Birmingham, United Kingdom, between 1950 and 19 54. The twins had their blood pressure measured and underwent an oral gluco se tolerance test. Results. There were no statistically significant associations between birth weight, length or ponderal index, and either blood pressure or glucose tole rance in the twins. Although there were substantial within-pair differences in birthweight between monozygous and dizygous twin pairs, these differenc es did not correlate with the adult outcomes. Monozygous correlations, howe ver, for both blood pressure and glucose tolerance were statistically signi ficantly higher than dizygous correlations and a quantitative genetic model suggested statistically significant heritability for these traits. In cont rast correlations of birthsize were similar in monozygous and dizygous pair s suggesting only a small genetic component in determining fetal size. Conclusion/interpretation. Our results show that birthsize in twins does no t predict adult blood pressure or glucose tolerance. We also suggest that s hared genetic determinants for fetal growth and adult outcomes are not like ly to be prevalent or powerful.