Gestational Hypertension Risk Up With SDB


SEATTLE — Sleep-disordered breathing is an independent risk factor for gestational hypertension, and it also may confer an elevated risk of adverse fetal outcomes, according to Louise M. O'Brien, Ph.D., of the Sleep Disorders Center at the University of Michigan, Ann Arbor.

SDB, often diagnosed clinically as habitual snoring, is common in women of childbearing age, with a reported prevalence of 5%-10%, Dr. O'Brien said at the annual meeting of the Associated Professional Sleep Societies. “This is probably the tip of the iceberg, because [many] women actually go undiagnosed.”

The anatomic and physiological changes of pregnancy make pregnant women uniquely vulnerable to SDB, she noted. Indeed, studies show that the prevalence of habitual snoring rises with pregnancy, and ranges from 10% to nearly 40% of women during the third trimester. Data from a large ongoing study at the University of Michigan show that habitual snoring is markedly more common in unselected women during the third trimester of pregnancy than in nonpregnant women (35% vs. 7%). “What was particularly interesting is that this wasn't driven by women who were snoring before they got pregnant; in fact, the majority started habitually snoring only after they reached the second trimester,” she said. This finding suggests that one-time screening shortly after conception will miss a lot of women.

Obesity appears to further elevate the risk. Compared with their normal-weight peers, obese women are more likely to have SDB in early pregnancy and to experience a worsening as pregnancy progresses (Chest 2001;120:1448-54.). In addition, weight gain during pregnancy that exceeds the amount recommended by the Institute of Medicine independently predicts SDB (odds ratio, 1.9), based on the results of a study in 2009.

When it comes to maternal outcomes, evidence has linked SDB to both gestational hypertension and pre-eclampsia, according to Dr. O'Brien. Women who habitually snore during pregnancy are twice as likely to have gestational hypertension as their nonsnoring counterparts (Chest 2000;117:137-41). In addition, the upper airway has been found to be narrowed in pregnant women and even more so among pre-eclamptic pregnant women compared with their nonpregnant peers (Am. J. Respir. Crit. Care Med. 2003;167:137-40).

Obesity complicates this picture because it also increases the risk of hypertension, she observed. But even after obesity is taken into account, habitual snoring remains an independent predictor of gestational hypertension (OR, 2.0), the 2009 study found. Moreover, there is an interaction whereby women who habitually snore and are obese have a particularly elevated risk (OR, 4.1).

On a brighter note, treatment of maternal SDB with continuous positive airway pressure (CPAP) may improve outcomes, Dr. O'Brien observed. For example, pregnant hypertensive women who snore and are at high risk of preeclampsia have a drop in blood pressure and maintain or reduce their dose of antihypertensive medication if they are treated with CPAP; in contrast, their blood pressure rises further and their dose of medication triples if they receive only usual care (Sleep Med. 2007;9:15-21). CPAP also appears to help restore the reduced fetal movements seen in women with preeclampsia (Sleep Med Clin. 2008;3:81-95).

Taken together, the evidence suggests that awareness of SDB during pregnancy is important, Dr. O'Brien stressed, yet obstetricians are generally unaware that their patients have habitual snoring or even apnea. “One, the women don't realize it's important to tell their physicians about it,” she said. “And two, the obstetricians don't realize its important to ask about it.”

Some surrogate measures of SDB may help obstetricians assess SDB-associated risk in their pregnant patients. For example, women are more likely to have gestational hypertension if they have a Mallampati grade of III or IV, indicating a crowded airway (OR, 1.9), or a neck circumference of 40 cm or greater (OR, 2.5), a 2008 study found. Dr. O'Brien reported that she had no conflicts of interest.

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