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Firstborn Women More Likely to be Obese?

Firstborn Women More Likely to be Obese?
  • Maybe being born second has its advantages. New research from Sweden suggests that firstborn women are more likely to be overweight or obese than their sisters. 

    Researchers analyzed data from the Swedish Birth Register on 13,500 pairs of sisters. The records included the participants' weight at birth, as well as their weight and height during their first prenatal visit of their first pregnancies.   

    The findings, published in the Journal of Epidemiology and Community Health, showed that the firstborn sisters weighted slightly less at birth than their following sibling, but as adults in their first trimester of pregnancy, the firstborns had higher BMIs - with an average of 24.4, compared to 23.8 for the second-borns.

    While the difference may seem slight, it is significant and, according to the researchers, translates to firstborn women being 29 percent more likely to be overweight and 40 percent more likely to be obese compared with their second-born sisters. 

    While the reason for the difference is still unknown, researchers speculate that the placenta may play a role.  Changes to the placenta may occur in later pregnancies; for instance, blood flow to the placenta increases in later births, meaning firstborns have a reduced nutrient supply. Less blood flow and nutrient supply to the placenta changes the regulation of fat and glucose, increasing the individual’s risk of storing more fat and having problems with insulin levels. 

    This isn’t the first study to show that firstborns are more susceptible to health risks; previous studies showed that adult men who are firstborns are at increased risk of insulin resistance and high blood pressure.  

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