Father's genes and lengthy pregnancies 5/5/03. By PB Research from Denmark shows that a father's genes can increase the risk of a lengthy pregnancy by 30 per cent.

Five per cent of all pregnancies last longer than the 37-41 week standard. Such late pregnancies put both mother and child at risk of greater health complications: the placenta, which passes oxygen and nutrients to the baby, may function less efficiently, or the baby may become too large to pass safely through the birth canal.

Annette Wind Olesen and colleagues at the University of Aarhus in Denmark looked at 22 000 women who, between 1980 and 1994, had a lengthy first pregnancy – lasting longer than 42 weeks – and then went on to have a second child. They found that those women who had a lengthy pregnancy for their first child had a 20 per cent higher chance of having a late pregnancy with their second child than those who had had a standard-length first pregnancy.

However, if the second child had a different father, the chance of the mother having a long second pregnancy was reduced by 30 per cent. A father can therefore increase the risk of a lengthy pregnancy by 30 per cent.

These results – published in the March 2003 issue of the British Medical Journal – show that the father’s genes may influence the timing of birth.

The researchers also looked at the impact of environmental factors, such as social status and area of residence, but found that a change in either of these factors had no affect on the length of the pregnancy.

The next step for the researchers could be to determine which genes are responsible for delaying birth, and whether there is an evolutionary advantage in being able to do so. It might be that late babies are more likely to survive after birth, for example. However, this advantage would have to be weighed against the increased risk posed to both mother and child of delivering a larger baby.

Image credit: Anthea Sieveking

Further reading

Olesen AW, Basso O, Olsen J. Risk of recurrence of prolonged pregnancy. BMJ. 2003 Mar 1;326(7387):476. Full text