PARIS -- A father's genes may influence the timing of his child's birth, according to a Danish study published in Saturday's issue of the weekly British Medical Journal (BMJ).

About five percent of births are late, a term defined as a pregnancy that lasts 294 days or more. The problem is known to cause health complications for mother and child, but exactly why it happens is an enigma.

The researchers looked at 43,000 births between 1980-92 among women who had had two children or more and whose first pregnancy had gone into extra time.

Only the first two deliveries were used in the analysis.

Overall, nearly 20 percent of the women who had had a prolonged first pregnancy had the same experience for their second child.

But this figure fell to just over 15 percent when the first and second child had different fathers.

"That's a lot," lead author Annette Wind Olesen told AFP. "It means that if you have the same partner for your second child, you have a 30-percent greater likelihood of a prolonged pregnancy compared with someone who changes partner."

Olesen, from the Danish Epidemiology Science Center in the University of Aarhus, says the figures are unlikely to be skewed by induced labor before 42 weeks, a practice that is rare in Denmark.

"Women had a reduced risk of recurrent post-term delivery if they changed partner between pregnancies," the study says. "We believe that this is a new observation. This result suggests that the timing of birth may, in part, be determined by paternal genes." The study also looked at 14,000 deliveries among women whose first child was born on schedule. Among this group, only seven percent of the second delivery was late. (AFP)