By Amy Norton
NEW YORK (Reuters Health) - 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 like blindness, deafness or cerebral palsy.
Of 1,394 baby boys, 23 percent died in the hospital, compared with 19 percent of girls.
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 percent of boys, versus 12 percent of girls.
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.
Kent and her colleagues report the results in the journal Pediatrics.
Pregnancy normally lasts about 40 weeks. Babies born before the 37th week are considered preterm, with those born before the 34th week being "early preterm." In the U.S., between three percent and four percent of births are early preterm.
It's well known that the earlier an infant comes into the world, the greater its risks of death or long-term health problems. It's not clear, though, why very early birth seems more dangerous for boys than girls.
The Y chromosome, which determines male sex, also influences certain health factors, Kent told Reuters Health in an email. It's known, for instance, that more male fetuses than female are lost to miscarriage.
"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," Kent said.
Another possibility, according to Kent, is that differences in boys' and girls' "cardiovascular responses" are at work.
Problems in the cardiovascular system, like blood pressure dysfunction, are more common the earlier an infant is born. If boys are less able to handle those problems, it might help explain why the gender gaps were seen in the very earliest births, but those gaps closed at week 27.
Kent said the most important thing for women is to go into pregnancy as healthy as possible, at a healthy weight and not smoking. She also advised getting good prenatal care and, if a woman notices changes that could signal preterm labor, she should tell her doctor right away.
Certain medications can be used to stop early contractions, buying time to treat the mother with steroid drugs that speed the development of the baby's lungs.
"If we are able to treat mothers with (prenatal) steroids 48 hours prior to delivery and magnesium sulphate four hours prior to delivery, we can reduce mortality and long-term neurological risk," Kent said.
The findings are based on records from 2,549 infants admitted to 10 neonatal intensive care units (NICUs) in Australia between 1998 and 2004.
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.
SOURCE: http://bit.ly/syTqxt Pediatrics, online December 19, 2011.