Can Stress During Pregnancy Affect the Size and Health of a Baby? One Study Says Yes

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One study shows that stress during pregnancy can affect the size and health of the baby.

Most women tend to have at least one worried thought throughout their pregnancy about their growing fetus. However, a new study conducted by scientists at the University of New Mexico and beyond now suggests that excessive stress can affect the size and health of the baby.

"The idea is that prenatal stress affects offspring in two different ways depending on the timing of the stressor during pregnancy -- yielding different outcomes before birth, after birth, and after weaning" explained study author, Andreas Berghänel, researcher at The University of New Mexico.

How are scientists concluding this happens? Prenatal maternal stress late in gestation causes mothers to invest less energy in their offspring, which leads to slower growth in the womb and during infancy. Once the baby has reached nutritional independence, however, they are no longer affected directly by their mother's provisioning, and then start to grow at the same rate as non-disadvantaged offspring. Thus, they maintain, maternal stress late in gestation leads to slow growth during dependent phases, but doesn't affect growth later.

By contrast, researchers say, prenatal maternal stress early in gestation can cause the fetus to be entirely reprogrammed to deal with a reduced life expectancy. To "make the best of a bad job," the early challenged offspring switches to an accelerated pace of life and grows and matures faster than unchallenged offspring to ensure that it reproduces before it dies. Once set on the fast track, the offspring under early prenatal maternal stress remain on this trajectory even after weaning and therefore overshoot the usual body size for age throughout development.

"Indeed, we’ve found that stress during late gestation reduces offspring growth during dependence, resulting in a reduced body size throughout development, whereas stress during early gestation results in largely unaffected growth rates during dependence but accelerated growth and increased size after weaning," says Berghänel.

All stressors noted appeared to have the same effect, he said. Whether mothers were exposed directly to stressors via food restriction or other adversities or were experimentally manipulated to increase their "stress hormones" for example, cortisol, the patterns of offspring growth across developmental stage relative to the timing of the stressor remained the same.

What do our IU Health experts have to say? “While stress can be a reality for everyone (not just women who are pregnant) and it’s something we should strive to reduce, I think the experts here are offering an overblown conclusion,” says Dr. Kelly Kasper, obstetrician and gynecologist at Indiana University Health. “Stress is a part of life and the reality is, pregnancy can be stressful.”

Dr. Kasper, who says she disagrees, with the study findings, also maintains that how we turn out as babies and ultimately fully developed people is a multifactorial process. “It’s not just based on one thing (like how stressed our mothers were when they were carrying us), it’s extremely multi-faceted, it’s genetics and how we are raised,” she says. “That said, excessive stress is not healthy for a pregnant woman—or any other individual, pregnant or not, so we should all strive to reduce it.”

The bottom line, says Dr. Kasper, is that women should focus on eliminating unnecessary stressors prior to and in pregnancy.

If there is a job, person or setting that stresses you out, make the chances that you need to, she says, to improve outcomes for you and your unborn child. “But don’t put incredible and unneeded pressure on yourself to always be calm, if you are carrying a child. Pregnancy can be challenging and some stress is normal.” 

-- By Sarah Burns

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