The Cause of Snoring in Pregnancy Reveald

Pregnancy and Snoring

Specialists know only too well, but the public is largely unaware that pregnant women, particularly in the third trimester, often snore heavily.

An Edinburgh research team has now discovered that the phenomenon is caused by a narrowing of the upper airways during pregnancy.

You may be surprised to hear it, but women are two or three times more likely to snore during pregnancy.

This is obviously a problem for the woman's partner and may cause tension within the couple at the very time when she most needs support, but it can also lead to health problems if the snoring becomes severe. Chronic snoring is known to be linked with respiratory problems at night, which can lead to daytime sleepiness, and can cause a rise in blood pressure, with attendant dangers not only for the mother, but also for the foetus, which may suffer growth retardation.

Yet, until now, little was known about the cause of snoring in pregnancy. So Neil Douglas and his colleagues at Edinburgh University decided to look into it more closely. Their prospective study, on 100 women who were at least 6 months pregnant and 100 control women of the same age range (between 18 and 41) has just been concluded, and the results appear in February's issue of the European Respiratory Journal (ERJ).

The study confirms, firstly, that women in the last trimester of pregnancy are more than twice as likely to snore (41%) than their non-pregnant counterparts (17%). It also shows that the percentage of snorers, among the pregnant subjects, rises from 12% before pregnancy to 41% during the third trimester.

However, the phenomenon proves to be reversible, since the proportion falls back to 18% three months after delivery, which is close to the proportion of snorers in the control group.

Moreover, the study examined another phenomenon linked with snoring, namely sleep apnoea, which was present in 14% of the pregnant subjects and only 3% of the control group.

Why does it happen?

Importantly, the Scottish study to be published in the next issue of the ERJ sheds light for the first time on some of the causes of the snoring so frequently encountered in late pregnancy.

In particular, there is a very clear link between a pregnant woman's weight and her likelihood of snoring. Compared to their non-snoring counterparts, pregnant snorers were found to have significantly higher pre-pregnancy weight and body mass index (+4kg and +2kg/m2 on average). Additionally, the pregnant women who snored tended to have a greater neck circumference, on average one centimetre more than that found in the non-snorers.

These differences subsist postpartum, whereas they are not present in the control group.

The Scottish team's most interesting discovery, however, concerned the upper airways. Using an original sound-wave method, Douglas and his colleagues carried out on each subject five successive measurements of the upper airways, in each of three positions (seated, lying on the back and lying on the side).

Narrower airways

During pregnancy, women's upper airways were narrower than when measured postpartum or compared to the control group. Since the measurements were conducted when the subjects were awake, it may be supposed that relaxation of the dilatory muscles during sleep would narrow the airways even further at night.

"This narrowing is caused by a physical phenomenon connected to increased weight and distention of the abdomen in pregnancy", Douglas explains. "Fat can infiltrate the pharyngeal muscles or be deposited in the soft tissue of the neck and around the upper airways, which can increase neck size and narrow the airways".

In pregnant women, systolic blood pressure rises as the airways become narrower. This discovery adds further strength to the data indicating that pregnant snorers have an increased risk of pre-eclampsia (of which arterial hypertension is a major feature).

So, as the Scottish team states in the ERJ, "it is likely that narrowing of the upper airways leads to a greater frequency of snoring and nocturnal respiratory disturbances in pregnant women, although the clinical significance of these changes remains to be studied.

"In the meantime, obstetricians should bear in mind that pregnant women may suffer from such troublesome snoring in the third trimester".

"However, given the social and medical significance of these problems, which is too often underestimated, it is important to reassure women by explaining that the process is reversible and providing appropriate treatment if necessary".

One simple way of reducing snoring, by example, is to sleep on one's side, but many pregnant women do this anyway. In extreme cases, mandibular advancement devices or a positive airway pressure masks may be considered.

Title of the original article: Sleep-disordered breathing and upper airway size in pregnancy and post-partum.