Stillbirths are more common among the heaviest and lightest fetuses, according to a new study from Canada.

Researchers found that 19 percent of all stillbirths occurred in fetuses whose weight put them in the lightest 10 percent of all fetuses of their age, with 6 percent of stillbirths occurring in the lightest 1 percent.

Fetuses among the heaviest 1 percent of those their age accounted for another 1 percent of all stillbirths.

“Extreme underweight and overweight states confer the highest risk of stillbirth,” the researchers wrote.

Stillbirth is commonly defined as death of a fetus after 23 weeks pregnancy and after the fetus weighs 500 grams (about 1.1 pounds); in this study, the researchers included fetal deaths that occurred after 20 weeks of pregnancy. The researchers collected data on all births in Ontario between 2002 and 2007 — a total of 767,016 live births and 4,697 stillbirths.

Problems with the placenta can result in a fetus being severely underweight, while fetuses are most at risk for being overweight if the mother is obese or has diabetes, according to the researchers.

The researchers say their finding may help doctors assess when it might be appropriate to deliver a baby early, in cases where the chance of it surviving outside the womb might be higher than the chance surviving in the womb.

In the developed world, stillbirths occur in 6 out of 1,000 births — a rate that is higher than the infant death rate from conditions such as sudden infant death syndrome or complications of premature birth, the researchers said.

The research was published yesterday (June 25) in the Journal of Perinatology.

Pass it on: Low or high fetal weight increases the risk of stillbirth.

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