Some Babies Deemed Overweight or Underweight at Birth Really Aren’t. Here’s Why

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A recent study, conducted by Dr. Joel Ray of St. Michael’s Hospital in Toronto, has concluded that birthweight can be influenced by both maternal and paternal ethnicity. It’s no secret that a baby’s birthweight is an important predictor of how he’ll handle the first few weeks of life. But you may not know that the way birthweight is measured isn’t entirely accurate — and it has to do with mom’s and dad’s ethnic backrounds.

Current birthweight curves, which compare a baby’s weight to other babies of his same age, are calibrated to assume that both parents are of Western European descent. This means that babies that are “normal” weight for their ethnic group could be classified as underweight or overweight based on the curves that are currently in use. For example, many babies who have a South Asian or East Asian mother or father may be deemed “underweight,” when really that’s not the case. They’re perfectly normal when compared to other babies of the same ethnicity, just not the curve that is generally used by doctors.

The study also looked at how birthweight was connected to where the parents lived. Immigrant parents who lived in a neighborhood with a high concentration of their same ethnic group, for instance, often gave birth to a baby who weighed less than a child of Canadian-born parents (the study was conducted in Canada, FYI).

Because Canadian birthweight curves only account for a single ethnicity, they are often inaccurate. Do you think your baby was inaccurately classified as underweight or overweight at birth? 

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