Birth Weights Drop, Surprising Researchers

A new study shows a drop in birth weights; C-sections and inductions could be partly to blame.

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Babies are being born a little lighter these days. Not much—an average of 1.8 ounces less in 2005 than in 1990, meaning the average birth weight of a baby born at full term today is just shy of 7½ pounds instead of a smidgen over, according to a study published Thursday in the journal Obstetrics & Gynecology. So why is this even worth reporting?

Well, the finding signals a reversal of a trend towards bigger and bigger babies that began after World War II. And, quite frankly, the Harvard University researchers who conducted the study were surprised. More pregnant women have factors that should increase their baby's birth weight: being older than 35, gaining more than 45 pounds during pregnancy, having diabetes before or during pregnancy, and avoiding smoking. Yet birth weights are dropping, not rising—particularly among women who have the lowest risk of having low-birth-weight babies to begin with: white, well-educated nonsmokers who received early prenatal care. These women's babies were born weighing an average of 2.8 ounces less in 2005 than in 1990.

Here's one factor that could be playing a role: the shift towards elective inductions of labor and scheduled cesarean sections that is causing an increasing number of babies to be born before their actual due date. (Babies typically gain an ounce a day during the last month of pregnancy.) [See more on the risky rise in C-sections.] "From 1990 to 2005, mean gestational length among U.S. term births decreased by more than 2 days, and the odds of birth on or after the 'due date' decreased by more than 40 percent," the study's authors wrote. But that's probably not the only factor, the researchers say; there could be some other reasons for the decline, still not identified, that could have a long-term negative impact on children's health. For now, though, no one is worrying too much about a few lost ounces in birth weight in otherwise healthy babies.

Another study came out this week that should make pregnant women smile. A review of five clinical trials published in the prestigious Cochrane Review found that there's no need for women to restrict food or beverages during labor. Those at low risk for complications had no differences in pregnancy outcomes whether they chomped only on ice chips or ate whatever their hearts desired. While I was never tempted to eat during my quick and nausea-inducing labors, I could certainly see the upsides to getting a little fuel for those laboring for eight, 12, or even 24 hours. If you're pregnant and worried about hunger pangs during labor, make sure to discuss this new finding with your doctor in advance.

Related news: swine flu advice for pregnant women and new moms.