Study ties race, sex to preemies' rate of survival

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Black premature baby girls born weighing 2.2 pounds or less are more than twice as likely to survive as white boys born at the same weight, a new study by University of Florida researchers has found.

The study, published Monday in the journal Pediatrics, also revealed that baby girls -- black and white alike -- had better survival prospects than boys when born weighing less than 2.2 pounds.

Research further showed that black female preemies with such a low birth weight are 1.8 times more likely to survive than their black male counterparts. It also found that premature black girls are 1.3 times more likely to live than premature white girls.

"When you're talking about survival," those differences are "very significant," said Dr. Steven B. Morse, a UF assistant professor of pediatrics and lead author of the report.

"We have known in general that females tend to have better survival rates than males, and blacks better than whites," he said. "But quantifying that and finding if there was a statistical significance had yet to be done."

Dr. Morse said it's still not clear why female and black premature infants have better chances of survival than boys and white infants born too soon.

But he suggested that part of the explanation could be that female preemies' lungs tend to be more developed at birth.

Dr. Herman A. Hein, professor of pediatrics at the University of Iowa, said prior research has shown that black women tend to have more premature babies than women of other races.

That is "possibly because their babies mature a little earlier and faster," which could explain why those infants have better odds of survival, he said.

For this study, UF investigators examined vital statistics from 5,076 premature babies weighing 2.2 pounds or less, who were born in Florida from 1996 to 2000. In some cases, the preemies weighed well less than a pound at birth.

He said researchers analyzed births that occurred as early as the first 21 weeks of pregnancy. About 1,500 preemies in the study were born when their mothers were less than 24 weeks pregnant.

"Overall, there was a survival rate of 60 percent among these babies who weighed less than [2.2 pounds] at birth," Dr. Morse said.

In this study, he said, the survival rate for infants born in the first 23 weeks of pregnancy was 27 percent. The rate doubled to 54 percent at 24 weeks, the researcher said.

Dr. Morse said preemies born when their mothers are less than 24 weeks pregnant are at highest risk for developing medical problems, such as cerebral palsy, blindness and chronic lung disease.

"There is a lot of controversy, especially at the lower gestational ages, of how much should we do for these babies, how aggressively should we treat them."

Dr. Morse said he and his research colleagues plan to study that issue next.