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Elective C-Section: 38th Week Too Soon

C-Section Before 39th Week Ups Baby Breathing Problems

Labor Good for Fetus

What does a C-section have to do with a newborn's ability to breathe?

As it leaves the liquid environment of the womb, a newborn faces the enormous challenge of making the transition to breathing air. Its fluid-filled lungs must clear quickly, Jain notes.

"There are many reasons why a baby born after elective C-section is more prone to delayed transition to air breathing," Jain says. "The first is reduced gestational age. And in the last trimester of pregnancy, every week counts. A 37-weeker is much more prone to respiratory issues than a 39-weeker."

Kirkeby Hansen and Jain note that during labor, a woman secretes powerful stress hormones. This triggers stress-hormone secretion in her fetus. The hormones have two effects on the fetal lungs. They speed the absorption of liquid. And they increase secretion of surfactants, natural substances that help clear liquid from the lungs.

"Once a woman is in labor, all this gets started," Kirkeby Hansen says. "In women who do not have labor, this process is not believed to start."

Jain says labor is the most reliable sign that a baby is ready to be born.

"When mother nature calls on spontaneous labor to start, it mostly is accurate in terms of the biologic clock and a good likelihood the baby is mature," he says. "But when we do it by elective C-section, we trust mothers' last-period dates or ultrasounds performed early in pregnancy, and those calculations are not always accurate."

Nearly a third of U.S. pregnancies now end in C-sections, Jain says. Over the last decade, as the C-section rate has climbed, the average gestational age at birth for U.S. babies has dropped from 40 weeks to 39 weeks.

On the one hand, Jain notes, research shows that delivering infants at 39 weeks' gestation or less cuts the risk of stillbirths. On the other hand, early delivery clearly has its own risks -- to the infant as well as to the mother.

"The obstetric community has to get its arms around the fact that C-section has never been proven to be safer for the mother," Jain says. "A study that appeared last year showed that when you look at mothers with no identified risk who have had a C-section -- with no medical indication either from the mother or from the fetus -- there was higher mortality in the mother and in the baby."

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