Babies born extremely early have much better survival odds now than in years past – but boys seem to be lagging behind girls, a new study finds.
Australian researchers found that of more than 2 500 infants born very preterm – in the 28th week of pregnancy or earlier – boys had a somewhat lower survival rate and were more likely to have long-term neurological problems.
Of 1 394 baby boys, 23% died in the hospital, compared with 19%.
The extreme preemie boys also had a higher rate of moderate to severe functional disability by the time they were three years old. Those problems – including blindness, deafness, cerebral palsy and mental retardation – affected nearly 20% of boys, versus 12% of girls.
More male foetuses lost to miscarriage
The gender gap seemed to disappear among infants born during the 27th or 28th week of pregnancy. But the researchers say the strength of that pattern is not clear, and it should be interpreted with caution.
The findings underscore that while much progress has been made in helping the tiniest preemies survive and thrive, those infants still face considerable risks, said Dr Alison L Kent, of Canberra Hospital and the Australian National University Medical School.
It's not clear why very early birth seems more dangerous for boys than girls. The Y chromosome also influences certain health factors, Dr Kent told Reuters Health in an email. It's known, for instance, that more male foetuses than female are lost to miscarriage.
Difference in sexes response to injury
"There is also evidence that there are sex differences in how the brain responds to injury, which may account for the differences in neurological outcome," she said. Another possibility, according to Dr Kent, is that differences in boys and girls have difference cardiovascular responses.
Dr Kent and her colleagues reported the results online December 19th in Paediatrics. The findings are based on records from 2,549 infants admitted to 10 neonatal intensive care units in Australia between 1998 and 2004.
Dr Kent said the results would likely be similar in other countries with NICU care comparable to Australia's. But since most of the infants were white, it's not clear if the findings would be the same in a more diverse population.
(Reuters Health, December 2011)