However, gestational ages aren't always perfect -- they're usually the obstetrician's best estimate, according to the study.
To assess whether other factors were also important in predicting a premature infant's chances for survival, researchers from the University of Texas Medical School at Houston and from the NICHD prospectively studied a group of more than 4,000 premature infants born between 22 and 25 weeks' gestation. Eighty-three percent were given intensive care in the hospital.
At follow-up between 18 and 22 months later, 61 percent of the babies had either died or had profound impairment.
In those infants who received intensive care, four factors emerged as being somewhat protective, in addition to increased gestational age. Receiving corticosteroids before birth, being female, being a singleton birth, and being a higher birth weight (per each 100 gram increase in weight), were all associated with a reduction in the risk of death and disability similar to the reduction seen with a one week increase in gestational age.
The study authors use an example of a baby born between the 24th and 25th week of gestation. For a female who is the appropriate weight for her gestational age, is a singleton birth, and who received corticosteroids before birth, the risk of death or profound impairment is 33 percent. But for a male who's small for his gestation age, didn't receive corticosteroids and who's a twin, the risk of death or profound impairment jumps to 87 percent, according to the study.
"Traditional teaching is that viability is 24 weeks, but what they're saying is here are other factors that are important. It's highlighting something that we've already known, that there's not a sharp line. It's all much grayer
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