Infant boys are a lot more trouble than infant girls when it comes to having a baby. If you want complications, then boys win the battle of the sexes hands down, according to research published today.
A team at The National Maternity Hospital, Holles Street, looked at more than 8,000 births, searching for an answer to something long understood by midwives - that boys cause more problems than girls. The results are published this morning in the British Medical Journal.
"As a humorous explanation for women in difficult labour, doctors often say, 'Oh, it must be a boy'," explained Dr Maeve Eogan, specialist registrar at Holles Street, who carried out the research with Dr Michael O'Connell, Dr Michael Geary and Dr Declan Keane. "That was the basis of the research; we wanted to see whether we were blaming males needlessly."
Now it's official - males really do cause more problems during labour, according to Dr Eogan's results. "We found that women who carried male infants had longer labours, more foetal distress and were more likely to require assistance during delivery.
"Some of these things can be explained because males are larger and have larger head circumferences" but this factor didn't fully explain the differences, she said. It may be that there was some "inherent vulnerability" in male babies. "They are more vulnerable to the effects of labour."
The team looked at first-time mothers who went into natural labour between 1997 and 2000.
Male births were much more likely to require the use of oxytocin, a hormone which stimulates contractions.
"Of the women carrying male infants, 70 per cent of them had completely normal deliveries, compared to 76 per cent of females."
Baby-boy labour averaged more than six hours, while average baby-girl labour lasted less than six hours. Forceps were needed in 23 per cent of boy births, but only 19 per cent of girl births.
"If there is evidence of an unusual foetal heart trace , we would then go on to do a foetal blood sample," Dr Eogan explained. Some 19.5 per cent of baby boys were sampled in this way, compared to 16.5 per cent of girls, her research found.
And while 6 per cent of boys were delivered by Caesarean section, only 4 per cent of girls were born this way.
She had no answers about why this should be so.
"The biological mechanisms can only be speculated on. We don't know why.
"It is one of those unknown variables," she concluded.