Late babies down to dad?

The timing of a baby's birth could be influenced by the father's genetic make-up, according to a new study of prolonged pregnancies. Researchers at the University of Aarhus in Denmark found that women who had an unusually long pregnancy were less likely to have a subsequent overdue baby if they had a different partner. The authors say their study, published in the British Medical Journal, suggests that birth timing may in part be determined by the father's genes.

Average pregnancies last for 40 weeks, but around 5 per cent last for 42 weeks or longer. To investigate possible causes of these prolonged pregnancies, the researchers compared 21,746 women who had an overdue baby with 7,009 women who had an average length pregnancy. Both groups had two or more children. They found that the risk of a second prolonged pregnancy in those women who had already experienced one was 19.9 per cent, compared to 7.7 per cent for women who had previously experienced a standard pregnancy. But for those women who had an overdue baby and then later had a baby with a new partner, the chances of another long pregnancy fell from 19.9 to 15.4 per cent.

'It was exciting to find out that there was a difference between fathers', said lead author Annette Wind Olesen. 'Knowledge about the birth mechanism is very sparse' she told New Scientist magazine.