A father's ethnic background may influence birthweight, according to a recent study.

Previous research from scientists at 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.

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.

For the study, researchers examined more than 692,000 births recorded with Vital Statistics in Ontario between 2002 and 2009.

"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," researchers said. "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.

The researchers said knowing how ethnic backgrounds impact birthweights is particularly important in Canada, given the growing number of mixed race families.

Researchers found that babies born to a foreign-born mother and a foreign-born father weigh about six percent less than children who were born to parents that were both born in Canada. They also found that 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.

Researchers 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, they said.

The findings were recently published Monday in the Journal of Epidemiology and Community Health.