Being an old ENT specialist, I saw many women who complained about nasal congestion and snoring during pregnancy. I wrote two blogs in 2017 that touched on snoring during pregnancy. One was on rhinitis (stuffy nose) of pregnancy, and the other was on sleep apnea during pregnancy.
The major cause of snoring during pregnancy is a stuffy nose. Snoring is partially obstructed and noisy breathing through your nose while sleeping. Snoring can range from just noisy breathing to loud snoring with brief periods of not breathing (sleep apnea). Doctors have a name that covers the range of snoring problems. It is called sleep disordered breathing (SDB). [1,2]
Since those blogs, quite a bit of new research on snoring and pregnancy has surfaced. In my blog on sleep apnea, I noted that snoring in pregnancy is linked to pregnancy high blood pressure, called preeclampsia. These new studies are linking snoring to other potential problems, including gestational diabetes, low birthweight babies, Cesarean section (C-section), and early labor. [2-4]
Don’t panic. Snoring during pregnancy is very common and the risk of a serious pregnancy problem is low. On the other hand, there are some simple things you can do to reduce snoring, so it is important to know about these new studies. The first thing you need to do is ask your sleep partner if you are snoring. [1,2] As Mark Twain said, “There ain’t no way to find out why a snorer can’t hear himself (or herself) snore.”
Why You Snore During Pregnancy
I already said that the major cause is a stuffy nose, but why does this happen during pregnancy? About four percent of women who are not pregnant are regular snorers.  Close to half of all pregnant women snore. Snoring usually starts late in the second trimester and continues through the third trimester. The main reason is pregnancy hormones. They can cause you to retain fluids in the linings of your nasal passages. This can also happen in the tissues of your throat. Both can contribute to snoring. [1,2]
Another factor that can contribute to snoring is weight gain. As your belly grows, it can push up against your lungs when you lie down to sleep. This can reduce your lung capacity and make it harder to breath. That extra effort can contribute to snoring. You could also be at higher risk for snoring when you are overtired, a common problem during pregnancy. When you don’t get enough sleep, you can fall into a deeper type of sleep that relaxes your throat muscles. This can narrow your airway. [1,2]
Researchers from Brown University have found a link between snoring during pregnancy and gestational diabetes. They looked at 1,000 pregnant women and found that women who snored during their third trimester had a significantly higher risk of gestational diabetes. 
Gestational diabetes is high high blood sugar during pregnancy. It can increase your risk of preeclampsia, preterm labor, and Caesarian section. Although this type of diabetes usually goes away after pregnancy, it may increase your long-term risk for developing type 2 diabetes. The researchers think that the stress of lower blood oxygen levels from snoring may decrease insulin production, or increase glucose release from the liver. 
Small Babies and C Sections
A study from the University of Michigan, that was published in the journal Sleep, looked at 1,673 women during their third trimester. Nine percent of women reported snoring almost every night before and during pregnancy. Twenty-six percent of the women reported snoring almost every night only during pregnancy. 
This study found that the women who were snoring before and during pregnancy had a higher risk of low birthweight babies and C-section than women who did not snore. The women who snored only during pregnancy had a higher rate of C-section than women who did not snore. 
Another study from the University of Michigan, also published in Sleep, found a link between snoring and early birth. The researchers questioned over 900 pregnant women about snoring in their third trimester. Fifty-two percent of the women reported frequent but quiet snoring. Six percent reported frequent and loud snoring. 
Quiet snoring did not affect time of delivery, but frequent loud snoring caused earlier delivery. The loud snoring women averaged close to one-week earlier delivery than all the other women in the study. 
Bottom Line on Snoring and Pregnancy
Nothing to panic about here, snoring during pregnancy is very common and pregnancy problems are rare. But the new studies support earlier studies linking snoring to pregnancy problems. Add gestational diabetes, C-sections, small babies, and early deliveries to the list along with preeclampsia. [1-4]
You just need to be aware of these risks. Find out about your nighttime breathing. Ask your partner or make a recording. Loud snoring and sleep apnea are the biggest risks. Let you pregnancy provider know about frequent snoring, loud snoring, or periods of apnea. You may need a sleep study to make sure you are not having dips in your blood oxygen levels during sleep. [1,2]
If you have sleep apnea, your doctor may suggest using a breathing device at night called CPAP (continuous positive airway pressure). For most pregnant snorers, simple solutions will do the trick to reduce snoring. Here are some tips: [1,2]
- Work with your doctor to maintain a healthy pregnancy weight.
- Stay active and get plenty of exercise.
- Ask your healthcare provider about ways to reduce nasal congestion at night. These include over-the-counter saline nasal spray, use of a saline solution with a Neti pot, and use of nasal strips or inserts that widen your nasal passages. Avoid decongestant nasal sprays and oral decongestants or antihistamines.
- Sleep on your side, not on your back.
- Raise the head of your bed by about 5 inches.
Remember, snoring may not start until the end of your second trimester. Make sure to ask your sleeping partner to listen to your breathing at night. If you become a frequent snorer or your snoring gets worse, talk to your pregnancy care provider. [1,2]
- American Thoracic Society, Sleep-disordered Breathing in Pregnancy.
- Research Features, The dangers of sleep disordered breathing in pregnancy.
- NHS, Pediatric Safety, Study: Snoring When Pregnant Linked to Low Birth Weight Babies.
- Sleep Research Society, Sleep, Snoring Frequency and Intensity in Pregnant Women and Association With Time to Delivery.