Snoring during pregnancy may be bad for the new baby’s health, according to research from the University of Michigan Health System.

Moms who snored three or more nights a week had a higher risk of poor delivery outcomes–including Cesarean births and delivering smaller babies–according to the research that appears in scientific journal Sleep.

Chronic snorers (moms who snored before and during pregnancy) are two-thirds more likely to have a baby that’s born below the tenth percentile for babies of the same gestational age compared to non-snorers. They are also more than twice as likely to need an elective C-section, researchers found.

“There has been great interest in the implications of snoring during pregnancy and how it affects maternal health but there is little data on how it may impact the health of the baby,” says lead author Louise O’Brien, PhD, MS, associate professor at U-M’s Sleep Disorders Center in the Department of Neurology and adjunct associate professor in the Department of Obstetrics & Gynecology at the U-M Medical School, in a statement. “We’ve found that chronic snoring is associated with both smaller babies and C-sections, even after we accounted for other risk factors. This suggests that we have a window of opportunity to screen pregnant women for breathing problems during sleep that may put them at risk of poor delivery outcomes.”

Timing of snoring patterns also made a difference in outcomes, researchers found. Chronic snorers who snored before and during pregnancy had the highest risks, being more likely to have smaller babies and elective C-sections. Meanwhile, those who started snoring only during pregnancy had higher risk of both elective and emergency C-sections than women who did not snore.

The study included 1,673 pregnant women who were recruited from prenatal clinics at U-M between 2007 and 2010, with 35 percent of the women reporting habitual snoring.

“Millions of healthcare dollars are spent on operative deliveries, taking care of babies who are admitted to the NICU, and treating secondary health problems that smaller babies are at risk for when grown,” O’Brien says. “If we can identify risks during pregnancy that can be treated, such as obstructive sleep apnea, we can reduce the incidence of small babies, C-sections, and possibly NICU admission that not only improves long term health benefits for newborns but also helps keep costs down.”