Cousin marriage and congenital anomalies in a multiethnic birth cohort

Congenital abnormalities (CAs) cause stillbirths, infant deaths and many later life disabilities. Infant mortality rates from different communities reflect levels of such birth defects and are often used to compare populations and determine key risk factors. Understanding causation and the high risk groups is clearly worthwhile, with a view to future prevention. Sheridan and his multidisciplinary team present results from a birth cohort collected from 2007 to 2011 in which data from 11,396 mothers, participating in the Born in Bradford study, were linked with details of 386 congenital anomalies identified (and validated) in the same period. This meant that putative risk factors for congenital anomaly could be compared with minimal bias and that confounding variables could be analysed separately. For example, earlier studies, associating higher rates of birth defect with frequent cousin marriages in British Pakistani families, were difficult to interpret since the methodologies did not take account of levels of social deprivation in different groups. This study gets that right. The core finding is confirmation that consanguineous marriage is a major risk factor for CAs, even after adjustment for deprivation. Specifically, increasing deprivation alone was not associated with higher congenital anomaly rates; nor was obesity and other nutritional disorders. Non-consanguineous couples (of all ethnic groups) had a CA rate of 2.5% compared with a rate of 6.5% for first cousins, giving a multivariate risk ratio of 2.19 (confidence interval 1.67-2.85). However, in all ethnic groups studied, maternal education level (diploma level or above) was correlated with lower CA rates.