Materials and Methods

This was a planned secondary analysis of a study that was designed to evaluate the prevalence of and trends in SDB across pregnancy among women at high risk for developing preeclampsia. We recruited women with prepregnancy body mass index (BMI) of 30 kg/m ² or greater, chronic hypertension, pregestational diabetes (type 1 or type 2), a prior history of preeclampsia, and/or a twin gestation. The study subjects were recruited as a convenience sample from ambulatory care practices at 2 university centers serving women with both private and public insurance.

After signing informed consent, women completed an at-home, overnight sleep evaluation with the Watch-PAT100 (Itamar Medical Ltd, Caesarea, Israel) during early pregnancy (between 6 and 20 weeks of gestation) and were asked to repeat the study in late pregnancy (between 28 and 37 weeks of gestation). The Watch-PAT 100, which has a peripheral arterial tonometry (PAT) finger plethysmograph and standard oxygen saturation (SpO ₂ ) probe, allows the recording of the PAT signal, heart rate, and oxyhemoglobin saturation. Sleep time is estimated using an inbuilt actigraph.

Analysis of these signals allows for the determination of an apnea hypopnea index (AHI), which is a sum of the number of apneas (breathing pauses) and hypopneas (shallow breathing) that occur per hour of sleep. In adults an AHI of 0-4.9 is considered normal and an AHI of 5 or greater defines SDB. An AHI of 5-14.9 is typically considered mild SDB, 15-29.9 moderate SDB, and 30 or greater severe SDB.

The Watch-PAT proprietary software algorithm was used to analyze the PAT signal amplitude along with the heart rate and SpO ₂ to estimate the AHI. An AHI event was scored if either a PAT amplitude reduction occurred with 3% or greater oxyhemoglobin desaturation or 4% or greater oxyhemoglobin desaturation occurred.

Studies in nonpregnant populations have shown that respiratory indices, such as the AHI, derived from the Watch-PAT are strongly correlated (r = 0.90) with those obtained from in-laboratory polysomnography (PSG) and also have demonstrated that the Watch-PAT is an accurate and reliable ambulatory method for the detection of SDB. O’Brien et al recently presented data comparing the Watch-PAT to full PSG in third-trimester pregnant subjects. Their results indicate that among pregnant women, the Watch-PAT AHI correlated very well with PSG AHI (r = 0.76, P < .0001) and that the Watch-PAT demonstrated excellent sensitivity (88%) and specificity (86%) for the identification of SDB in pregnancy.

All participants received obstetrical care by their physicians, who were unaware of the sleep study results. However, women were informed if their AHI was 10 or greater and given contact information for sleep specialists in the area if they were interested in further evaluation. Given that there are currently no sanctioned pregnancy-specific guidelines for SDB treatment or evidence that treatment in the short term has an impact on maternal, obstetric, or neonatal outcomes, no alteration of care was recommended or mandated for study participants, regardless of AHI.

Pregnancy outcomes were abstracted from the medical record by physicians unaware of the SDB status of the study subjects. Outcomes of interest included preeclampsia, gestational diabetes, preterm birth (<34 weeks’ gestation), and birthweight. Preeclampsia was divided into the following categories in concordance with American College of Obstetricians and Gynecologists guidelines: (1) mild preeclampsia, which was new-onset systolic blood pressure of 140 mm Hg or greater or a diastolic blood pressure of 90 mm Hg or greater on 2 occasions 6 hours apart on or after 20 weeks 0/7 days of gestation and within 72 hours of a diagnosis of proteinuria (≥300 mg in a 24-hour urine collection, a spot protein creatinine (PC) ratio of 0.2, or the finding of ≥2+ on dipstick if a 24-hour urine or PC ratio was not available) ; (2) severe preeclampsia in which criteria for mild preeclampsia are met plus 1 or more of the following: blood pressure of ≥160 mm Hg systolic or ≥110 mm Hg diastolic on 2 occasions at least 6 hours apart, proteinuria of ≥5 g, cerebral or visual disturbances, pulmonary edema or cyanosis, epigastric or right upper-quadrant pain, impaired liver function, thrombocytopenia, and/or fetal growth restriction; or (3) superimposed preeclampsia, which in a woman with hypertension before 20 weeks of gestation is a sudden increase in proteinuria if already present in early gestation, a sudden increase in hypertension, or the development of HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome.

All diagnoses of preeclampsia were confirmed by a second physician. Gestational diabetes was diagnosed according to glucose tolerance test standards (either a 100 g, 3-hour glucose tolerance test or a 75-g, 2-hour glucose tolerance test). Women with pregestational diabetes were excluded from the gestational diabetes analyses.

Associations were explored between SDB presence/severity and our outcomes of interest through the use of the χ ² , Fisher exact, and χ ² test for trend for categorical variables. Multivariable logistic regression was used to adjust for potential confounders. All tests were 2 tailed and a P < .05 was considered statistically significant. Statistical analysis was performed using SPSS 19.0 statistical software (SPSS Inc, Chicago, IL).

For the primary study, designed to detected changes in SDB across pregnancy, we established that a sample size of 180 women would be required to complete the baseline study. We enrolled 233 women; 182 had valid sleep study data and delivered at the study sites. The incidence of early pregnancy SDB in this high-risk population was 30%. Assuming a 15% risk of preeclampsia in our non-SDB subjects and an α of 0.05, we had 80% power to detect an increase to 34% (crude odds ratio, 2.9) among women with SDB. This magnitude of association is consistent with that that has been observed between SDB and cardiovascular and metabolic diseases in nonpregnant individuals. This study was approved by the Institutional Review Board of Northwestern University and North Shore University Health System.

Results

Two hundred thirty-three women consented to participate in the primary study. One hundred eighty-eight and 128 of these women had a valid early and late pregnancy sleep study, respectively. The reasons for incomplete sleep data are presented in the Figure . The mean gestational age (±SD) was 16.7 ± 3.5 and 32.6 ± 2.4 weeks at the first and second sleep study, respectively.

Study recruitment

Facco. Sleep-disordered breathing in pregnancy. Am J Obstet Gynecol 2014 .

Demographic characteristics of the study population are provided in Table 1 . Sixty-two percent of subjects were obese, 30% had chronic hypertension, 57% had pregestational diabetes, 15% had prior preeclampsia, and 6% had a twin gestation. Fifty-four percent of women had more than 1 qualifying risk factor. In early pregnancy 21%, 6%, and 3% of women had mild, moderate, or severe SDB, respectively. These frequencies increased to 35%, 7%, and 5% in the third trimester. Twenty-seven percent of participants (n = 34) experienced a worsening of SDB during pregnancy; 26 were cases of new-onset SDB, whereas the other 8 had SDB in early pregnancy that worsened in severity. Because of the small number of cases of moderate and severe SDB, we combined these 2 groups for further analysis.

Pregnancy outcomes were available for 182 of the 188 women with a valid early pregnancy sleep study. Two women had first trimester miscarriages, and 4 women were lost to follow-up.

The rates of adverse pregnancy outcomes stratified by SDB status are presented in Tables 2 and 3 . Preeclampsia occurred in 17.6% of women (14 cases of mild preeclampsia, 6 cases of severe preeclampsia, and 12 cases of superimposed preeclampsia). There was no relationship demonstrated between SDB in early or late pregnancy and preeclampsia. The rate of preterm birth less than 34 weeks was 9%, of which half were iatrogenic. There was no relationship demonstrated between SDB exposure in early or late pregnancy and either preterm birth less than 34 weeks or iatrogenic preterm birth less than 34 weeks. Similarly, there was no association between SDB and extremes of birthweight (less than 5% or greater than 95% for gestational age).

Table 3

SDB in late pregnancy and adverse pregnancy outcomes

Variable	No SDB	Mild SDB AHI 5-14.9	Moderate/severe SDB AHI ≥15	P value a
Any preeclampsia	13/67 (19.4)	4/45 (8.9)	2/16 (12.5)	.2
Preeclampsia among women without CHTN	10/50 (20)	3/33 (9.1)	1/7 (14.3)	.3
Superimposed preeclampsia among women with CHTN	3/17 (17.6)	1/12 (8.3)	1/9 (11.1)	.6
Gestational diabetes	4/25 (16)	5/14 (35.7)	5/11 (45.5)	.05
Preterm birth <34 wks	5/67 (7.5)	1/45 (2.2)	0/16 (0)	.1
Iatrogenic preterm birth <34 wks	4/67 (6)	1/45 (2.2)	0/16 (0)	.2
Birthweight
<5%	1/67 (1.5)	0/44 (0)	0/16 (0)	.4
>95%	13/67 (19.4)	1/44 (25)	2/16 (12.5)	.9

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