Women who sleep on their backs in the later months of pregnancy may have a relatively higher risk of stillbirth if they already have other risk factors, a new study suggests. Experts stressed that the findings do not prove that sleep position itself affects stillbirth risk. "We should be cautious in interpreting the results," said UTMB's Dr. George Saade. "We can't conclude that sleeping on the back causes stillbirth, or that sleeping on your side will prevent it," said Saade, who was not involved in the study. It is, however, plausible that back-sleeping could contribute, Saade said. Lying on the back can exacerbate sleep apnea, and if a fetus is already vulnerable, that reduced oxygen flow could conceivably boost the odds of stillbirth, he explained.