July 2, 2012 -- Earlier-term infants may have an increased risk for learning delays, a new study shows.
When researchers compared gestational age at birth to academic test scores in third grade, they found that children delivered at 37 and 38 weeks' gestation had lower scores than children delivered in their 39th, 40th, or 41st gestational week.
The differences were small. But the findings suggest that even among babies considered full-term -- defined as delivery at 37-41 weeks -- gestational age at delivery may influence development years later.
The study could also have important implications for the timing of C-sections performed for non-medical reasons, the researchers say.
One in three babies born in the U.S. is now delivered by cesarean section -- a more than 50% increase since 1996.
Researcher Howard F. Andrews, PhD, of Columbia University, says pregnant women and their doctors should consider the possibility of learning delays when deciding on the timing of elective C-sections.
"This study is certainly not the last word, but it does suggest a potential risk for developmental delays among term infants born at 37 or 38 weeks," Andrews tells WebMD. "Even if the risk is small, why would you want to take it for a C-section that isn't medically necessary?"
Test Scores Lower in Earlier-Term Babies
The study, published online today in the journal Pediatrics, included data on more than 128,000 children born in New York City between 1988 and 1992.
All the children were delivered between 37 and 41 weeks' gestation, and all attended New York City public schools in third grade.
The researchers matched birth records with the children's scores on standardized third-grade reading and math tests.
Compared to children born at 41 weeks gestation:
Children born at 37 weeks had a 23% increased risk of having at least a moderate reading impairment in third grade.
Birth at 38 weeks' gestation was associated with a 13% increase in risk for at least moderate reading difficulties.
A similar pattern was seen for math scores, but little difference in scores was recorded in babies born in their 39th, 40th, or 41st gestational week.
Time to Redefine Full Term?
The impact was independent of other risk factors for learning delays, including low birth weight and family economic status.
Pediatrician Roya Samuels, MD, of the Cohen Children's Medical Center in New Hyde Park, N.Y., says the findings, if confirmed, could change the thinking about what full term really means.
"Thirty-seven weeks has been our marker for when a baby is full term, and most of the research on developmental delays has been on babies born earlier than this," she tells WebMD. "This suggests that it may be worth taking a closer look at babies born in that 37- and 38-week window."
She adds that while other research will be needed to confirm the findings, the scientific evidence in favor of delaying non-medically necessary C-sections is mounting.
"Every week in utero is another week of growth and development," she says. "It is definitely prudent to wait as long as you can if you are considering an elective C-section for non-medical reasons."