Soon-to-be mothers who snore during pregnancy put not only their own health at risk but also the health of their newborn — increasing their risk of low birth weight and delivery by C-section, according to a recent study.

Women start to snore during pregnancy because of nasal congestion, the increase in abdominal girth, and the uterus pressing on the diaphragm, according to the National Sleep Foundation. The increased swelling in the nasal passages blocks the airways and therefore causes the sleeper to snore. If the blockage is severe, sleep apnea — loud snoring and periods of stopped breathing during sleep — may result, which can bring health complications to women and their newborns. The Mayo Clinic says that C-sections may be performed if a mother is diagnosed with high blood pressure while pregnant — which can be brought on by snoring — and make labor dangerous.

This commonly tends to be a problem in a woman’s third trimester of pregnancy. but it is not yet known how widespread it is.

Publishing in the journal Sleep, researchers from the University of Michigan Health System recruited 1,673 pregnant women in their third trimesters (weeks 29 and over) to examine the impact of maternal snoring during pregnancy on key delivery outcomes. Mothers were asked whether they habitually snored and were then followed up to observe their birth outcomes. In the study, habitually snoring was defined as snoring three to four nights per week or nearly every night.

Thirty-five percent of the participants self-reported habitual snoring: 26 percent started to snore in pregnancy, and nine percent were chronic snorers (those who snored before and during pregnancy). The findings showed that habitual snoring was associated with a high outcome of having a low birth weight baby and a C-section.

Chronic snorers were two-thirds more likely to have a baby whose weight was in the bottom 10 percent, and also twice as likely to need elective C-section delivery compared to non-snorers, reports The Guardian.

In the U.S., about one in every 12 babies is born with low birth weight. When a baby is classified as having a low birth weight, typically he or she is born weighing less than5 lbs, 8 oz. March of Dimes reports that two main reasons why babies may be born with low birth weight is premature birth (before 37 completed weeks of pregnancy) or fetal growth restriction (baby doesn’t gain the weight he or she should before birth).

"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,” said Louise M. O’Brien, Ph.D., M.S., lead author of the study and associate professor from the University of Michigan's Sleep Disorders Centre.

The researchers of the study speculate that snoring leads to increased levels of inflammation, which could affect the placenta and lead to low birth weight. This theory warrants further investigation. What's more, the study did present an obvious limitation. The snoring was self-reported, which lends to the possibility that other women who snored were not aware of their own snoring.

In a similar study published in the American Journal of Obstetrics and Gynecology, researchers found that frequent snoring played a role in blood pressure problems, even after other known risk factors were accounted for. High blood pressure in pregnancy can lead to preeclampsia, which is associated with low birth weight, higher risk of pre-term birth, and babies ending up in the intensive care unit (ICU).

To learn more about snoring during pregnancy, click here.