(HealthDay News) – The risk of stillbirth is increased at extreme percentiles of birth weight across all gestational ages, according to a study published online May 17 in the Journal of Perinatology.

Joel G Ray, MD, and Marcelo L Urquia, PhD, from the University of Toronto, examined the risk of stillbirth in a population-based study involving 767,016 liveborn and 4,697 stillborn singletons delivered between 20 and 41 weeks’ gestation in Ontario, from 2002–2007. The sex-specific absolute birth weight differences were calculated for stillborns versus liveborns at different gestational ages.

At the 10th percentile the researchers found that, starting at 24 weeks of gestation, stillborns weighed significantly less than liveborns. By 32 weeks, the difference was 590 and 551 grams for males and females, respectively. Across all gestational ages there was a reverse J-shaped correlation between the percentile birth weight and the risk of stillbirth. Compared with the 40th to 60th percentile, birth weight at <1st percentile and at ≥99th percentile had an increased likelihood of stillbirth (adjusted odds ratio, 9.63 and 2.24, respectively). The increased risk of stillbirth at extreme percentiles of birth weight was seen for all gestational ages.

“Sizeable birth weight differences were observed between stillborns and newborns, starting at about 24 weeks’ gestation, and following a reverse J-shaped pattern,” the authors write. “This same pattern was observed for the risk of stillbirth in association with the lower and upper extremes of birth weight, especially, at the very lowest percentile, and was not appreciably affected by maternal age or parity.”

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