Children born too early show lower test scores in school, according to a new study published in Pediatrics. Even babies who are technically born at term — at 37 or 38 weeks — do worse than those who are delivered later.
Although a pregnancy is considered full term at 37 weeks, at which point experts say babies are developed enough to breathe on their own, doctors are increasingly recommending that women delay giving birth until 39 weeks if they can, because babies do a lot of critical development in those last two weeks. Yet many expectant moms, who still don’t know that full-term pregnancies should last 39 weeks, have been opting for elective cesarean sections earlier, thinking that it’s safe.
Preterm birth has long been known to put children at risk for developmental problems down the line, but the Pediatrics study offers fresh evidence that even being born before 39 weeks, which is technically term, may have lasting effects on babies.
In the study, researchers led by Dr. Kimberly Noble at Columbia University looked at 128,050 babies born between 37 weeks and 41 weeks gestation in New York City between 1988 and 1992. The researchers compared the length of pregnancy to the children’s scores on standardized reading and math tests when they were in third grade.
Kids born later did better: children born at 37 or 38 weeks had significantly lower achievement scores than those born at 39, 40 or 41 weeks. Specifically, compared with children born at 41 weeks, those born at 37 weeks had a 14% greater risk of having a mild reading impairment and a 33% higher risk of having a severe reading impairment by the third grade. The same effect was found for math: kids born at 37 weeks had a 16% greater risk of having a mild impairment in performing basic math skills, such as computation or estimation, compared with children born at 41 weeks. For each additional week of gestation, the scores improved.
The trend held even after the scientists adjusted for potential confounders such as the babies’ birth weight, the amount of prenatal care the mother received, and even socioeconomic factors, such as the mother’s education, race and history of substance abuse, all of which are known to influence children’s test scores and academic achievement.
“As pediatricians, we are taught that full term is 37 weeks,” says Noble, noting that this is based primarily on physical attributes. “But our data suggest that children born at 37 weeks and 38 weeks have an increased risk of academic performance problems compared to children born at 39 weeks or 40 weeks. So we recommend exercising caution in inducing delivery prior to 39 weeks.”
Noble’s study adds to the growing body of research focusing on babies’ crucial development between 37 and 41 weeks. Previous studies have shown that babies born at 37 weeks have twice the risk of death as those who don’t come out until 40 weeks. Full-term babies, born at 39 weeks or later, feed better, weigh more and have fewer vision and hearing problems than those born slightly earlier. They also have bigger brains: between 37 weeks and 41 weeks, the brain continues to grow, boosting grey matter, or the amount of nerves, by 50%; white matter, which includes the neural connections that these nerves make, increases threefold.
While Noble acknowledges that her study could not determine why the babies were born before 39 weeks — such as whether the moms had voluntarily decided to induce labor, or whether an underlying medical condition prompted the earlier birth — the findings add to the evidence that the traditional definition of full-term pregnancy may need revision.
The results should help both mothers and doctors appreciate that not all “term” infants are the same, she says, especially when it comes to cognitive outcomes later in life; those couple of weeks between 37 and 39 weeks may make a bigger difference than previously thought. As with many other good things in life, therefore, delaying delivery may be worth the wait.