We studied pregnant women of white, European ancestry from two studies (Table 1). The ALSPAC study (23) is a prospective study, which recruited pregnant women from Bristol, UK, with expected delivery dates between April 1991 and December 1992. The EFSOCH study (20) is a prospective study of children born between 2000 and 2004, and their parents, from a geographically defined region of Exeter, UK. All women gave informed consent and ethical approval was obtained from the ALSPAC Law and Ethics Committee and the local review committee for each study.
