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Stress During Pregnancy Affects Size of Baby

Summary: A new study reveals prenatal stress has a physical effect on babies. Researchers report prenatal maternal stress in late gestation leads to slower growth of the offspring both in utero and during infancy.

Source: University of New Mexico.

A new study has been published that suggests babies are physically affected by the stress level of their mother during pregnancy. It has been previously found that adversity in the womb enhances or hampers offspring development and performance.

Researchers from The Universities of New Mexico and Göttingen, as well as the German Primate Center, have now proposed a hypothesis that largely predicts why there are highly variable patterns in the growth rates of disadvantaged offspring across 719 studies on 21 mammal species.

“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” says Andreas Berghänel, evolutionary anthropologist at The University of New Mexico and lead author of the study.

For example, prenatal maternal stress late in gestation causes mothers to invest less energy in their offspring, which leads to slower grow 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 consequently grow at the same rate as non-disadvantaged offspring. Thus, maternal stress late in gestation leads to slow growth during dependent phases, but doesn’t affect growth later.

By contrast, prenatal maternal stress early in gestation additionally causes 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.

In combination, an infant’s acceleration of their developmental processes together with a deceleration due to reduced maternal investment could then cancel each other out during phases of intense maternal investment—gestation and lactation. It is not until the infant is nutritionally independent that the programming effects become clear.

This new comparative study finds all of these predictions are supported in a large sample of studies that each measured the effects of prenatal stress on offspring size and growth compared to an unchallenged control group.

“We 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.

a pregnant woman

In combination, an infant’s acceleration of their developmental processes together with a deceleration due to reduced maternal investment could then cancel each other out during phases of intense maternal investment—gestation and lactation. It is not until the infant is nutritionally independent that the programming effects become clear. NeuroscienceNews.com image is in the public domain.

All stressors seem to have the same effect, and the results are stable across a variety of experiments. 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.

Significance

These new results may bear some translational value for understanding why girls start their menstrual cycles earlier in poorer neighborhoods, why teenage pregnancies are more frequent in disadvantaged families, and why adverse conditions during early development, particularly in formula-fed children, often lead to obesity and other metabolic health problems later in life.

Maternal stress during gestation causes numerous effects on infant physiology that extend well into adulthood. Empirical tests of this hypothesis across mammals suggest that the timing of the stressor during gestation and a simultaneous consideration of maternal investment and adaptive growth plasticity effects are crucial for a full comprehension of prenatal stress effects on offspring growth. The results support an adaptive life history perspective on maternal effects that is relevant for evolutionary biology, medicine, and psychology.

About this neuroscience research article

Source: Katie Williams – University of New Mexico
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “Prenatal stress accelerates offspring growth to compensate for reduced maternal investment across mammals” by Andreas Berghänel, Michael Heistermann, Oliver Schülke, and Julia Ostner in PNAS. Published online November 27 2017 doi:10.1073/pnas.1707152114

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University of New Mexico “Stress During Pregnancy Affects Size of Baby.” NeuroscienceNews. NeuroscienceNews, 29 November 2017.
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University of New Mexico (2017, November 29). Stress During Pregnancy Affects Size of Baby. NeuroscienceNews. Retrieved November 29, 2017 from http://neurosciencenews.com/pregnancy-stress-baby-size-8053/
University of New Mexico “Stress During Pregnancy Affects Size of Baby.” http://neurosciencenews.com/pregnancy-stress-baby-size-8053/ (accessed November 29, 2017).

Abstract

Prenatal stress accelerates offspring growth to compensate for reduced maternal investment across mammals

Across mammals, prenatal maternal stress (PREMS) affects many aspects of offspring development, including offspring growth. However, how PREMS translates to offspring growth is inconsistent, even within species. To explain the full range of reported effects of prenatal adversity on offspring growth, we propose an integrative hypothesis: developmental constraints and a counteracting adaptive growth plasticity work in opposition to drive PREMS effects on growth. Mothers experiencing adversity reduce maternal investment leading to stunted growth (developmental constraints). Concomitantly, the pace of offspring life history is recalibrated to partly compensate for these developmental constraints (adaptive growth plasticity). Moreover, the relative importance of each process changes across ontogeny with increasing offspring independence. Thus, offspring exposed to PREMS may grow at the same rate as controls during gestation and lactation, but faster after weaning when direct maternal investment has ceased. We tested these predictions with a comparative analysis on the outcomes of 719 studies across 21 mammal species. First, the observed growth changes in response to PREMS varied across offspring developmental periods as predicted. We argue that the observed growth acceleration after weaning is not “catch-up growth,” because offspring that were small for age grew slower. Second, only PREMS exposure early during gestation produced adaptive growth plasticity. Our results suggest that PREMS effects benefit the mother’s future reproduction and at the same time accelerate offspring growth and possibly maturation and reproductive rate. In this sense, PREMS effects on offspring growth allow mother and offspring to make the best of a bad start.

“Prenatal stress accelerates offspring growth to compensate for reduced maternal investment across mammals” by Andreas Berghänel, Michael Heistermann, Oliver Schülke, and Julia Ostner in PNAS. Published online November 27 2017 doi:10.1073/pnas.1707152114

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