THURSDAY, June 28, 2012 (HealthDay News) -- Fetuses at the extremes of weight -- either very small or very large -- have a greater risk of being stillborn than babies of more average weight, a new study indicates.
Researchers from St. Michael's Hospital in Ontario examined records of about 767,000 live births and nearly 4,700 stillbirths that occurred in Ontario between 2002 and 2007. Stillbirth is typically defined as a fetus that dies at the 23rd week of gestation or later and weighing at least 1.1 pounds, though this research included fetuses that died at 20 weeks or later.
About 19 percent of stillbirths occurred in fetuses below the tenth percentile for weight, meaning they are smaller than 90 percent of fetuses.
The smallest fetuses faced an even bigger risk. Being among the smallest 1 percent put fetuses at a nearly 10 times higher risk of stillbirth than average weight babies, or those in the 40th to 60th weight percentiles.
Very large fetuses also faced some added risks. About 1 percent of stillbirths occurred among fetuses in the top 1 percent for weight.
"In this study of all registered live-born and stillborn infants in Ontario, extreme underweight and overweight states confer the highest risk of stillbirth," study authors Drs. Joel Ray and Marcelo Urquia, said in a hospital news release.
Small fetuses are often due to a faulty placenta, while maternal diabetes and obesity often leads to very large fetuses. The rate of stillbirth in industrialized countries is about six per 1,000.
The study was published June 25 in the Journal of Perinatology.
The U.S. National Institutes of Health provides more information on stillbirth.