Women are more likely to suffer a tough labour if they are giving birth to a baby boy rather than a baby girl, says a study.

This has long been an "old midwives tale" based on years of experience of troublesome births but until now no-one had tried to test its truth.

Research carried out at Dublin's National Maternity Hospital suggests that deliveries of baby boys do seem more likely to involve extra intervention from doctors, such as forceps, drugs, or emergency caesarean section.

Something like 52% of all babies are boys, but the rate of perinatal mortality is higher Spokesman, National Childbirth Trust

The researchers looked at more than 8,000 births - half male, half female - all of which were first babies from mothers who went into labour naturally at full term.

Labours involving male infants tended to last longer, and far fewer were delivered in a straightforward natural way.

Among the boys, there were 249 caesarean sections, as opposed to 170 among the girls, and 925 uses of the forceps or ventouse compared with 771 among the girls.

Big heads

A potential explanation given by the researchers was that the head size of the boys tended to be larger, perhaps presenting more difficulties during labour.

However, there are other factors which have as much if not more bearing on this than head circumference - such as the anatomy of the mother, the position of the babies, and the force of the contractions.

A spokesman for the National Childbirth Trust said it was not surprising that boy babies encountered more problems.

She said: "We have known for a long time that a high proportion of boys die during labour, are stillborn, or, unfortunately, die within a month of delivery.

"Something like 52% of all babies are boys, but the rate of perinatal mortality is higher."

The study was published in the British Medical Journal.