MARRIAGE BETWEEN FIRST cousins can more than double the risk of those couples giving birth to a baby who will have a congenital defect, but researchers have cautioned that the absolute risk is low.
The multi-ethnic study of more than 11,396 babies from the Yorkshire city of Bradford in the UK between 2007 and 2011 is published in The Lancet medical journal today.
It found that consanguinity – marriage between blood relatives – is a major risk factor for congenital anomalies such as heart and lung defects or down syndrome.
“The risk remains even after adjustment for deprivation, and accounts for almost a third of anomalies in babies of Pakistani origin,” the researchers from the University of Leeds said.
Marriage between blood relatives is common within the large Pakistani community based in Bradford with about 37 per cent of Pakistani marriages being between first cousins, according to the study.
These account for nearly a third – 31 per cent – of birth anomalies in babies of Pakistani origin. Researchers caution that the absolute risk of birth defects is small – between 3 and 6 per cent.
“Only a small minority of babies born to couples who are blood relatives or older mothers will develop a congenital anomaly,” lead author Eamonn Sheridan from the University of Leeds said.
The study identified older white British mums as having an increased risk of having babies with birth defects – between 2 and 4 per cent – but researchers said this was expected.
The study looked at various maternal and clinical risk factors such as smoking, obesity and deprivation in children with one or more anomalies (ie birth defects) but found the greatest risk factor was closely-related parents.
Overall rates of congenital anomalies in babies born in Bradford and included in the study were almost double – 305.74 per 10,000 livebirths – than the national average in the UK – 165.90 per 10,000.
Researchers said that the socioeconomic status of Bradford did not alone explain the increased rate of anomalies in the babies of blood relatives, despite the fact that two-thirds of the babies come from the most deprived fifth of the UK population.
They also found that a high level of maternal education roughly halved the risk of having a baby with a congenital anomaly, irrespective of ethnic origin.