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Developmental Biology - Low Birth Weight

Do You Get Easily Out of Breath?

Perhaps you were small at birth, a new study suggests...


Babies born with low birth weights are more likely to have poor cardio-respiratory fitness later in life than normal-weight peers. This is according to a study by researchers at Karolinska Institutet in Sweden published in the Journal of the American Heart Association JAHA.
These findings underscore the importance of prevention strategies aimed at reducing low birth weights, even among babies carried to term.

Having good cardio-respiratory fitness the ability to supply oxygen to muscles during sustained physical activity is important for staying healthy and reducing risk of numerous diseases as well as premature death.

Given its alarming impact on public health, there is growing interest in understanding underlying causes for poor cardio-respiratory fitness. Both physical inactivity and genetic factors are important as determinants.
Cardio-respiratory fitness is declining globally, both for youth and adults. A recent study shows the proportion of Swedish adults with low cardio-respiratory fitness almost doubled from 27 percent in 1995 to 46 percent in 2017.

Preterm delivery and the low birth weight associated with it, is also linked to low cardio-respiratory fitness later in life. In this study, researchers wanted to examine if low birth weight plays a role in cardio-respiratory fitness for individuals born after 37 to 41 weeks of pregnancy.

They followed more than 280,000 males from birth to military conscription at age 17-24 using Swedish population-based registers. At conscription, the men underwent a physical examination that included an evaluation of their maximal aerobic performance on a bicycle ergometer. The researchers found that those born with higher birth weights performed significantly better on the cardio-respiratory fitness test. For every 450 grams of extra weight at birth, in a baby born at 40 weeks, the maximum work capacity on the bicycle increased by an average of 7.9 watts.

The association was stable across all categories of body mass index (BMI) in young adulthood and largely similar to a subset analysis of more than 52,000 siblings, suggesting BMI and shared genetic and environmental factors alone cannot explain the link between birth weight and cardio-respiratory fitness.
"The magnitude of difference we observed is alarming. They observed 7.9 watts increase for each 450 grams of extra weight at birth in a baby born at 40 weeks, translates into approximately 1.34 increase in metabolic equivalent (MET) associated with a 13% difference in the risk of premature death and a 15% difference in risk for developing cardiovascular disease. Such mortality differences are similar to the effect of a 7-centimeter reduction in waist circumference."

Daniel Berglind, researcher at the Department of Global Public Health at Karolinska Institutet and corresponding author.

Researchers believe their findings are significant to public health as approximately 15% of babies born globally weigh less than 2.5 kilos at birth. Also, as cardio-respiratory fitness has important implications on adult health.
"Providing adequate prenatal care may be an effective means of improving adult Health not only through prevention of established harms associated with low birth weight but also via improved cardio-respiratory fitness."

Viktor H. Ahlqvist PhD, Department of Global Public Health, and a study author.

Abstract
Background
Preterm delivery and low birth weight are prospectively associated with low cardio-respiratory fitness (CRF). However, whether birth weight, within the at-term range, is associated with later CRF is largely unknown. Thus, the aim of the current study was to examine this issue and whether such association, if any, is explained by shared and/or nonshared familial factors.

Methods and Results
We conducted a prospective cohort study, including 286 761 young male adults and a subset of 52 544 siblings born at-term. Objectively measured data were retrieved from total population registers. CRF was tested at conscription and defined as the maximal load obtained on a cycle ergometer. We used linear and nonlinear and fixed-effects regression analyses to explore associations between birth weight and CRF. Higher birth weight, within the at-term range, was strongly associated with increasing CRF in a linear fashion. Each SD increase in birth weight was associated with an increase of 7.9 (95% CI, 7.88.1) and 6.6 (95% CI; 5.97.3) Wmax in the total and sibling cohorts, respectively. The association did not vary with young adulthood body mass index.

Conclusions
Birth weight is strongly associated with increasing CRF in young adulthood among men born at-term, across all categories of body mass index. This association appears to be mainly driven by factors that are not shared between siblings. Hence, CRF may to some extent be determined already in utero. Prevention of low birth weight, also within the at-term-range, can be a feasible mean of increasing adult CRF and health.

Authors
Viktor H. Ahlqvist, Margareta Persson, Francisco B. Ortega, Per Tynelius, Cecilia Magnusson and Daniel Berglind.


Acknowledgments
Berglind conceived and designed the current study and wrote and was involved in data analyses. Ahlqvist performed the statistical analyses and was involved in manuscript editing. Tynelius was involved in statistical analyses. Persson, Ortega, and Magnusson critically revised the manuscript and commented on the statistical analyses. All authors approved the final manuscript.

The study was funded by the Stockholm County Council.


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Feb 6 2020   Fetal Timeline   Maternal Timeline   News 



Normal weight baby on the right side of two below weight babies. The findings are significant to public health, as about 15 percent of babies born world wide weigh less than 2.5 kilos at birth. Their cardio-respiratory fitness has important implications on their adult health.
CREDIT Ron Sutherland/science Photo Library.


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