Apart from being annoying to household members, snoring during gestation poses serious threat to a mother and a fetus. Scientists from Michigan report in the American Journal of Obstetrics & Gynecology (1) (AJOG) that pregnancy-onset snoring is independently associated with gestational hypertension and preeclampsia. According to WHO both conditions are the leading causes of maternal and neonatal morbidity (2). Researchers admit that, although the mechanism of this relationship is unclear, the treatment of habitual snoring alone might significantly reduce the risk of complications during pregnancy.
The “Sleep Heart Health Study”(3, which was published in 2001, has provided evidence that sleep-disordered breathing (SDB) has a large impact on cardiovascular health of human organism. SDB stands for a spectrum of respiratory irregularities ranging from habitual snoring to obstructive sleep apnea. Previous observations were confirmed – there is strong association between SDB and hypertension, as well as metabolic dysfunction.
It is well-known that overweight, which causes the growth of the neck circumference, is a risk factor of any SDB. It has been estimated that 10% increase in weight predicted a 6-fold increase in the odds of developing moderate-to-severe SDB (4). Obviously, most pregnant women gain even more than 10% of initial weight. This seems to contribute to the relatively high incidence of snoring during gestation (5). Unfortunately, SDB has a detrimental effect also on pregnant women’s health. However, the latest paper in AJOG is thought to be the first large, prospective study to show that pregnancy-onset snoring, but not chronic, plays the biggest part in this scenario.
The described research was designed as a cohort study, which enrolled 1673 pregnant women of age, more than 28 weeks pregnant. A comparison group was formed of 202 non-pregnant women. They were recruited from prenatal and gynecological clinics of University of Michigan. Women filled in a specially prepared questionnaire, which asked about their age, race, Body Mass Index (BMI) before pregnancy, current BMI, smoking status, medical history and family history of hypertensive disorders.
Most importantly, participants were asked about “habitual snoring”, which was defined as 3-4 episodes per week, and the time of its onset. Researchers decided that this simple question was enough, as they have already found (6) that women who reported snoring “usually” or “often” had sleep-disordered breathing (SDB) confirmed later in overnight polysomnogram test.
Michigan scientists found that pregnant women were more than twice as likely as controls to snore. Around 34% of women in third trimester reported snoring and great proportion of them started having symptoms of SDB only during pregnancy. Comparison between pregnant women with and without snoring showed that the non-snoring were significantly slimmer. The ones that started snoring during pregnancy had the most weight gain and suffered from gestational hypertension and preeclampsia more often than those who reported snoring also before pregnancy.
The latter were however the most obese and most likely to have chronic hypertension. Nearly one forth of chronic snorers were smokers. Apart from hypertension and preeclampsia, the independent association was confirmed towards gestational diabetes (GDM). Surprisingly this relationship was not observed according to women, who began snoring during pregnancy. In addition, high pre-pregnancy BMI was a predictor of GDM and preeclampsia, while excessive weight gain only for preeclampsia. Furthermore scientists counted that around 19% of gestational hypertension and about 12% of preeclampsia could be eliminated in the population if pregnancy-onset snoring was ameliorated.
The presented study has many strengths but the reason is unknown why snoring, which starts during pregnancy, causes hypertension and preeclampsia. Moreover, pathogenesis of preeclampsia alone is poorly understood. Endothelial dysfunction, oxidative stress and inflammation seem to play a key role. It is thought that pathogenic process starts in the placenta during early pregnancy (7). As snoring begins usually in the second or third trimester of pregnancy, this might not explain preeclampsia. So authors of the study speculate if pregnancy-onset snoring exacerbates underlying inflammation and cardiovascular dysfunction through excessive activation of sympathetic nervous system. One way or another, consolation is that, according to preliminary studies, continuous positive airway pressure (CPAP) may improve blood pressure in pregnancy (8).
Written by: Natalia Neumann
Source:
1.O’Brien LM, Bullough AS, Owusu JT et al. Pregnancy-onset habitual snoring, gestational hypertension, and preeclampsia: prospective cohort study. Am J Obstet Gynecol. 2012 Sep 7.
2.Khan KS, Wojdyla D, Say L et al. WHO analysis of causes of maternal death: a systematic review. Lancet
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4.Peppard PE, Young T, Palta M et al. Longitudinal study of moderate weight change and sleep-disordered breathing. JAMA 2000;284:3015-21.
5.Franklin KA, Holmgren PA, Jonsson F et al. Snoring, pregnancy-induced hypertension, and growth retardation
of the fetus. Chest 2000;117:137-41.
6.O’Brien LM, Bullough AS, Hewlett MM et al. Associations between habitual snoring and polysomnogram-defined SDB in pregnant women. Sleep 2011;34:A320.
7.Powe CE, Levine RJ, Karumanchi SA. Preeclampsia, a disease of the maternal endothelium:
the role of antiangiogenic factors and implications for later cardiovascular disease. Circulation 2011;123:2856-69.
8.Poyares D, Guilleminault C, Hachul H, et al. Pre-eclampsia and nasal CPAP, part 2: hypertension
during pregnancy, chronic snoring, and early nasal CPAP intervention. Sleep Med 2007;9:15-21.
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