Objective
This study aimed to prospectively examine the impact of chronic vs pregnancy-onset habitual snoring on gestational hypertension, preeclampsia, and gestational diabetes.
Study Design
Third-trimester pregnant women were recruited from a large, tertiary medical center from March 2007 through December 2010 and screened for the presence and duration of habitual snoring, as a known marker for sleep-disordered breathing. Clinical diagnoses of gestational hypertension, preeclampsia, and gestational diabetes were obtained.
Results
Of 1719 pregnant women, 34% reported snoring, with 25% reporting pregnancy-onset snoring. After adjusting for confounders, pregnancy-onset, but not chronic, snoring was independently associated with gestational hypertension (odds ratio, 2.36; 95% confidence interval, 1.48–3.77; P < .001) and preeclampsia (odds ratio, 1.59; 95% confidence interval, 1.06–2.37; P = .024) but not gestational diabetes.
Conclusion
New-onset snoring during pregnancy is a strong risk factor for gestational hypertension and preeclampsia. In view of the significant morbidity and health care costs associated with hypertensive diseases of pregnancy, simple screening of pregnant women may have clinical utility.
Sleep-disordered breathing (SDB), a spectrum of respiratory abnormalities during sleep ranging from habitual snoring to obstructive sleep apnea, is common yet often undiagnosed, especially in women. Increased weight promotes SDB and, strikingly, a weight gain of only 10% has been associated with a 6-fold increase in the development of significant SDB. This observation is particularly relevant to pregnancy as weight gain >10% occurs in most women. Habitual snoring, the hallmark symptom of SDB, increases during pregnancy and is particularly common in preeclampsia.
The cardiovascular implications of untreated SDB are substantial and complex. Several large, population-based studies such as the Sleep Heart Health Study and the Wisconsin Sleep Cohort Study have provided clear evidence for an independent association between SDB and cardiovascular disease, particularly hypertension and metabolic dysfunction. The Nurses Health Study found that snoring increased the risk of incident hypertension independent of age or body mass index (BMI). The mechanisms linking SDB and cardiovascular disease are likely multifactorial, involving sympathetic overactivity, inflammation, and endothelial dysfunction.
Hypertensive disorders of pregnancy are a leading cause of maternal and infant morbidity and cost billions of dollars annually to treat. An emerging literature of cross-sectional studies support an association between SDB and hypertension during pregnancy. The association between SDB and hypertension is particularly relevant during pregnancy as such morbidities jeopardize the health of mother and fetus, with major public health impact. Furthermore, new-onset SDB during pregnancy conceivably could have health ramifications that exceed those of chronic SDB, to which cardiovascular systems might have time to adapt. An improved understanding of some vulnerabilities unique to pregnancy may offer opportunities to improve the health of both mothers and infants.
The goals of this study were to determine the prevalence and incidence of snoring during pregnancy and to examine associations with maternal health. We hypothesized that snoring, and especially pregnancy-onset rather than chronic snoring, would be associated with gestational hypertension, preeclampsia, and gestational diabetes.
Materials and Methods
In this prospective study, pregnant women were recruited from prenatal clinics within the University of Michigan from March 2007 through December 2010. Women were eligible if they were ≥18 years old and ≥28 weeks pregnant with a single fetus. There were no other exclusion criteria. Written informed consent was obtained to access medical records. A comparison group of nonpregnant control women was recruited from women aged 18-45 years attending routine gynecology visits. This study was approved by the University of Michigan Institutional Review Board.
Pregnant women completed a questionnaire about the presence of habitual snoring and whether they had “stopped breathing or gasped for air” ( Appendix , Supplementary Figure ). They were also asked whether a bed partner had complained. Habitual snoring was defined as snoring at least 3-4 times per week. Similarly witnessed apneas were considered present if women “stopped breathing or gasped for air” at least 3-4 times per week. Enquiry was made about the timing of snoring to identify incident cases. Pregnancy-onset snoring was considered present when habitual snoring began during pregnancy. Chronic snoring was defined as habitual snoring both before and during pregnancy. A single question about snoring was chosen instead of a multi-item SDB questionnaire for several reasons: a single question is strongly and reliably associated with the overnight polysomnogram (PSG)-derived apnea/hypopnea index (number of apneic events per hour of sleep) ; in women a report of “often” or “usually (always or almost always)” snoring is associated with PSG-confirmed SDB with respective odds ratios (ORs) of 3.8 and 16.3 20 ; its use provides an approach easily and immediately translated into clinical settings; no study has failed to associate snoring with objective measures of SDB from a PSG; validation of complex SDB screening tools in pregnancy has not been performed; most SDB scales emphasize weight, which in pregnancy will be necessarily high; and several scales rely on gender or hypertensive status, the major outcome in the current study. Nonpregnant women completed the same screening tools, with the exception of symptoms in relation to pregnancy. Pregnant women received a $10 gift card for participating.
Prepregnancy BMI was calculated from maternal self-report of height and weight just prior to conception and cross-checked with documented BMI from the initial obstetric visit in the first trimester. Serial weights throughout the pregnancy were obtained from clinical visits and, following delivery, the total amount of weight gain was calculated. Key variables abstracted from medical records included demographics, individual or family history of gestational hypertension or preeclampsia, smoking status, and the presence of a diagnosis of chronic hypertension, gestational hypertension, preeclampsia, or gestational diabetes. The latter diagnoses were obtained from medical coding using the International Classification of Diseases, Ninth Revision . In reporting this study, guidelines from Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) group were followed.
Statistics
Sample size was calculated based on literature available at the time of study design. We predicted the frequency of snoring as 4% in nonpregnant women and 25% in pregnant women. With a sample size ≥1400 pregnant women and 200 controls there would be a power of almost 100% to detect this difference with a 2-tailed significance level of 5%. If the frequency of snoring in nonpregnant women was 16% and that in pregnant women remained at 25%, the targeted sample sizes would provide 82% power to detect a difference. We anticipated that approximately 4% of women without snoring would develop hypertension compared to 10% of women with snoring. Thus a test for equal frequency of hypertension based on this study (test for equality of binomial proportions) would have power of >95%. We planned to recruit unequal group sizes because the nonpregnant controls would serve only as a comparison for frequency of snoring.
As BMI is strongly associated with SDB, and BMI changes across pregnancy, prepregnancy or early first-trimester BMI was categorized according to Institute of Medicine (IOM) recommendations. Subjects were classified as underweight (BMI <18.5 kg/m 2 ); normal weight (BMI 18.5-24.9 kg/m 2 ); overweight (BMI 25.0-29.9 kg/m 2 ); or obese (BMI ≥30.0 kg/m 2 ). Absolute weight gain was determined and subjects were classified according to whether they exceeded the IOM recommendations for gestational weight gain; 28-40 lb for underweight women, 25-35 lb for normal-weight women, 15-25 lb for overweight women, and 11-20 lb for obese women.
All data obtained were double-entered into a database to ensure accuracy and analyzed with software (SPSS, version 18.0, IBM Corp, Armonk, NY). Histograms, box plots, and descriptive methods were used to examine data for errors and outliers. Between-group comparisons of continuous variables (maternal age, BMI, and gestational age) were conducted with t tests (snoring vs no snoring) and analysis of variance (chronic snoring, pregnancy-onset snoring, and no snoring). Dichotomized variables were compared with χ 2 tests. Logistic regression was used to determine associations between snoring and maternal outcomes after adjusting for potential covariates (maternal age, race, prepregnancy BMI, weight gain in excess of IOM recommendations, gravidity, smoking, educational level, individual or family history of gestational hypertension/preeclampsia). OR and 95% confidence intervals (CIs) were calculated. A P value < .05 was considered statistically significant. Population attributable risk percent (PAR%) was calculated; this represents the proportion of disease (hypertension/preeclampsia) among the total population that would not have occurred in the absence of exposure (snoring), assuming that the exposure contributes in a causal manner to the disease. The following formula was used:
P A R % = ( i n c i d e n c e t o t a l _ p o p u l a t i o n − i n c i d e n c e u n exp o s e d ) / i n c i d e n c e t o t a l _ p o p u l a t i o n
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