Is birth weight related to ethnicity?

New research on average newborn birth weight and family ethnicity finds that one size does not fit all.

Photo: Getty Images
Photo: Getty Images

With my Chinese heritage and small stature, I expected my newborn daughter to be on the wee side, but not super tiny, what with her father’s Ukrainian and Irish genes in the mix. Even though I delivered her at full-term, her birth weight was only six pounds, 14 ounces, which is less than the national average of approximately seven pounds, six ounces, but significantly higher than five pounds, eight ounces — the current cut-off for babies deemed “low birth weight” (or LBW). This number does not take ethnicity or family traits into account. So why does this matter? Babies classified as low birth weight, or small for gestational age (SGA), are actually at risk for what doctors call short-term morbidity, a label that can sound alarming to new parents who are already overwhelmed by caring for their little one. Plus, newborns usually drop a bit more weight from fluid loss before gaining it back in the first couple of weeks.

“The reason we identify babies as SGA is because we suspect they didn’t reach their growth potential due to a hostile uterine environment of some kind. We want to monitor them closely after birth for any health consequences,” explains Gillian Hanley, a post-doctoral fellow studying maternal and child health at the University of British Columbia.

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Her 2013 study with co-researcher and UBC professor Patricia Janssen looked at how birth weight varies by ethnicity. They examined data from more than 100,000 newborns against different birth-weight standards: a population-based chart (established primarily with white babies from 1981 to 2000) and two other newer charts that accounted for ethnicity (one for Chinese babies and one for South Asian babies). “We found that the ethnicity-specific chart better identified the babies that most need the attention of health practitioners,” she affirms. Many of the Chinese and South Asian babies who were labelled small in the population-based distributions were actually perfectly healthy when compared to the ethnicity-specific distributions.

Todd Sorokan, a paediatrician and neonatologist in Surrey, BC, sees a high percentage of South Asian newborns at his hospital. “We know that South Asian babies are often slimmer and smaller than other ethnic groups. And it’s an important study, because with limited healthcare resources, it is good to try to identify kids with higher risk.” He’s careful to point out that a baby’s small size is not always due to ethnicity or genetics, so doctors will still look at other potential underlying causes, such as mothers who may not have had enough protein or iron in their diets. “We may just not be doing a good enough job with maternal health,” Sorokan explains. In other words, he sees potential for improved healthcare with the additional ethnicity data, but still proceeds with caution, taking a case-by-case approach. “We will still treat babies individually. As paediatricians, we’re a bit leery to say, ‘Oh, the baby is small, but he’s South Asian, so that’s OK.’”

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Hanley says that adding the ethnicity factor to the equation could help better direct healthcare resources to those most in need and decrease stress for parents. “Our results suggest that we can do a better job appropriately identifying which babies really do require additional monitoring, and many parents can be saved from unnecessary anxiety and concern.”

Vancouver mom Mary Isaac was surprised when her full-term baby girl, Adelayde, weighed in at only five pounds, six ounces. “You hear so many things about how small babies can struggle with a multitude of things — breathing, feeding, growth and development,” she says. “A new mother has enough to worry about!” Thankfully, her midwife’s assurances kept her from worrying, and she says Adelayde soon “fattened up.”

“Remember that just because your baby is small doesn’t mean there is something wrong,” Isaac adds. “Or that you did anything wrong.”

A version of this article appeared in our December 2013 issue with the headline “Small talk,” pp. 80.

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