Father's ethnic background influences birthweight, study finds

Previous research by Dr. Joel Ray of St. Michael's Hospital has shown that a mother's ethnic background can influence birthweights, and his team's new study shows the same is true for a father.

Dr. Ray, a physician and researcher at the hospital's Li Ka Shing Knowledge Institute, has studied birthweights among different ethnic groups because babies who are considered to be small or large just before birth can trigger medical interventions such as Cesarean deliveries. Birthweight is also one of the essential yardsticks used to measure a baby's progress in its first days and weeks after birth.

Current birthweight curves--graphs used to plot how one baby's weight compares to others of the same age -- assume that the parents are of Western European descent. That means many babies of an East Asian or South Asian mother may be classified as underweight, when in fact they are "normal" for their ethnic groups. The new study shows the same is true when the father is of Asian descent.

Knowing how ethnic backgrounds impact birthweights is particularly important in Canada, given the growing number of mixed race families. Researchers led by Dr. Joel Ray, have developed the first "newborn weight curves" for specific ethnic groups across Canada, but using only the mother's ethnicity.

Dr. Ray's new paper, published in the Journal of Epidemiology and Community Health, shows that babies born to a foreign-born mother and a foreign-born father weigh about six per cent less than those whose both parents were born in Canada.

Babies of a Canadian-born mother and foreign-born father weigh quite a bit less than those of two Canadian-born parents. Babies of a Canadian-born father and a foreign-born mother weigh somewhere in between.

Dr. Ray also looked at whether birthweights were affected by where the parents lived. When immigrant parents live in neighborhoods with a high concentration of people from their same ethnic background, their babies weigh less than those of Canadian-born parents. This is particularly true for male babies, he said.

Dr. Ray's study was based on an examination of 692,301 births recorded with Vital Statistics in Ontario between 2002 and 2009.