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 the scientific journal Sleep. The study is believed to be the largest of its kind to link maternal snoring to baby health by following moms from pregnancy through delivery.

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 (smaller than 90 percent of other babies the same gestation) 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, Ph.D., M.S., 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.

"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.

Snoring is a key sign of obstructive sleep apnea, a sleep-related breathing problem that can reduce blood oxygen levels during the night and has already been associated with serious, expensive health conditions. The new research comes a year after another study led by O'Brien showed that women who begin snoring during pregnancy are at high risk for high blood pressure and preeclampsia.

Pregnant women can be treated for obstructive sleep apnea using CPAP (continuous positive airway pressure). The method involves a machine worn during sleep that uses air pressure to keep the airways open.

"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," says O'Brien, who is also an associate research scientist in the Department of Oral & Maxillofacial Surgery.

"If we can identify risk factors 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 improve long term health benefits for newborns but also help keep costs down."