Objective
The objective of the Sleep Disordered Breathing substudy of the Nulliparous Pregnancy Outcomes Study Monitoring Mothers-to-be (nuMoM2b) is to determine whether sleep disordered breathing during pregnancy is a risk factor for adverse pregnancy outcomes.
Study Design
NuMoM2b is a prospective cohort study of 10,037 nulliparous women with singleton gestations that was conducted across 8 sites with a central Data Coordinating and Analysis Center. The Sleep Disordered Breathing substudy recruited 3702 women from the cohort to undergo objective, overnight in-home assessments of sleep disordered breathing. A standardized level 3 home sleep test was performed between 6 0 -15 0 weeks’ gestation (visit 1) and again between 22 0 -31 0 weeks’ gestation (visit 3). Scoring of tests was conducted by a central Sleep Reading Center. Participants and their health care providers were notified if test results met “urgent referral” criteria that were based on threshold levels of apnea hypopnea indices, oxygen saturation levels, or electrocardiogram abnormalities but were not notified of test results otherwise. The primary pregnancy outcomes to be analyzed in relation to maternal sleep disordered breathing are preeclampsia, gestational hypertension, gestational diabetes mellitus, fetal growth restriction, and preterm birth.
Results
Objective data were obtained at visit 1 on 3261 women, which was 88.1% of the studies that were attempted and at visit 3 on 2511 women, which was 87.6% of the studies that were attempted. Basic characteristics of the substudy cohort are reported in this methods article.
Conclusion
The substudy was designed to address important questions regarding the relationship of sleep-disordered breathing on the risk of preeclampsia and other outcomes of relevance to maternal and child health.
Sleep-disordered breathing (SDB) refers to conditions that are characterized by abnormal respiratory patterns (eg, apneas, hypopneas) and abnormal gas exchange (eg, hypoxemia) during sleep. Obstructive sleep apnea (OSA), the most common type of SDB, is characterized by repetitive episodes of airway narrowing during sleep that lead to respiratory disruption, hypoxemia, and sleep fragmentation. Self-reported snoring and daytime sleepiness, which reflects turbulent airflow and sleep disruption, respectively, are cardinal symptoms of OSA. Although these sleep-related complaints are common in pregnancy, there are very few studies that comprehensively and objectively have evaluated the prevalence, incidence, severity, or outcomes that are associated with OSA in pregnancy. Also, these studies have not evaluated other major, although less common, sleep-related breathing disorders such as central apnea and sleep-related hypoventilation and hypoxemia.
Objective assessment of SDB requires in-laboratory or home sleep testing. SDB generally is diagnosed with the use of the Apnea Hypopnea Index (AHI), a sum of the number of apneas (cessation of airflow) and hypopneas (pathologic limitation but not cessation of airflow) that occur per hour of sleep. In nonpregnant adults, an AHI score of ≥5 is a minimum criterion for defining SDB. Severity is classified by the number of events per hour (AHI score of 5-15 is considered mild SDB; >15-30 is considered moderate SDB, and >30 is considered severe SDB. SDB, most commonly OSA, occurs in 2-15% of middle-aged adults, but there are certain populations that are at greater risk. SDB may occur as often as 40% in obese individuals, and 70-90% of morbidly obese individuals are thought to have the disorder.
Epidemiologic data from cohorts of generally middle-aged and older adults (none of which included pregnant women) indicate that SDB is associated with incident and prevalent cardiovascular and cerebrovascular diseases and adverse events. Both cross-sectional and prospective studies reported associations between SDB and hypertension. Data from the Wisconsin Sleep Cohort Study demonstrated a dose-response association between SDB at baseline and the presence of hypertension 4 years later that was independent of known confounding factors (age, sex, body mass index [BMI], and waist and neck circumference). In this study, relative to the reference category of an AHI score of 0 events per hour at baseline, the adjusted odds ratios (ORs, 95% confidence intervals [CIs]) for hypertension at follow-up evaluation were 2.03 (95% CI, 1.29–3.19) with an AHI score of 5.0–14.9 and 2.89 (95% CI, 1.46–5.64) with an AHI score of ≥15 ( P = .002, trend test). Other studies have reported associations between SDB and coronary artery disease, stroke, cardiac arrhythmia, heart failure, and cardiovascular disease–related death. SDB also is associated with type 2 diabetes mellitus. Cross-sectional data from the Wisconsin Sleep Cohort Study demonstrated that self-reported diabetes mellitus was 3-4 times more prevalent in subjects with an AHI score of ≥15 than in those with an AHI score of <5. Another large prospective cohort study demonstrated that moderate-to-severe SDB was an independent risk factor for incident diabetes mellitus.
The prevalence, incidence, and severity of SDB in pregnancy and the impact of SDB on pregnancy remain undetermined. This is despite the fact that pregnant women may be particularly predisposed to OSA and other major sleep-related breathing disorders, because of the physiologic changes that are associated with the gravid state. Pregnancy is the only normal adult physiologic process in which bodyweight routinely increases by ≥20% in a short period of time. The high estrogen levels that are associated with pregnancy can cause vasomotor rhinitis. Hyperemia and edema of the nasal and pharyngeal mucosa can lead to increased airflow resistance and airway narrowing. Finally, uterine enlargement, diaphragmatic elevation, and relaxation of costochondral ligaments lead to alterations in thoracic shape, in compliance, and in capacity predisposing to ventilatory impairment. In fact, SDB symptoms are common during pregnancy and worsen as the pregnancy progresses. The prevalence of frequent snoring (≥3 nights/week) in general obstetrics populations has been reported to be approximately 7-11% in prepregnancy/early-pregnancy states and 16-25% in the third trimester. In addition, outcomes that have been linked to SDB in the nonpregnant population, such as hypertension and insulin-resistant diabetes mellitus, have correlates in pregnancy (eg, gestational hypertension [GH], preeclampsia, gestational diabetes mellitus [GDM]). Moreover, SDB has been linked to enhanced inflammatory and oxidative stress responses, endothelial damage, and metabolic derangements. These same biologic pathways have been associated with adverse pregnancy outcomes.
In a large retrospective cohort study, Bourjeily et al found that frequent snoring was associated with GH/preeclampsia, even after adjustment for multiple factors that included BMI that was assessed at delivery (adjusted OR [aOR], 2.3; 95% CI, 1.4–4.0). In a large retrospective cohort of women with polysomnography-confirmed SDB within 1 year before pregnancy (n = 791, compared with 3955 age-matched control subjects), Chen et al reported that SDB was associated with an increased risk of GH (aOR, 3.18; 95% CI, 2.14–4.73), GDM (aOR, 1.63; 95% CI, 1.07–2.48), and preterm birth (aOR, 2.31; 95% CI, 1.77–3.01). This study, which used data that were derived from Taiwan’s National Health Insurance databases, adjusted for obesity with the use of International Classification of Diseases 9th edition codes, but only 1.6% of this population was identified as obese. In a recent metaanalysis of studies, Pamidi et al reported that maternal SDB was associated significantly with GH/preeclampsia (pooled aOR, 2.34; 95% CI, 1.60–3.09; 5 studies) and GDM (pooled aOR, 1.86; 95% CI, 1.30–2.42; 5 studies). Such data underscore the potential importance of SDB to pregnancy outcomes and the importance of gaining a better understanding of the epidemiologic factors of this disorder in pregnancy. However, most research regarding the epidemiologic factors of SDB in pregnancy is retrospective, and most studies have relied on self-reported symptom assessments rather than objective measures. Many studies did not control adequately for obesity, which is a strong risk factor for both SDB and adverse pregnancy outcomes, nor did they clearly define a temporal relationship between SDB and the subsequent development of preeclampsia and GDM. There are no large studies that have examined SDB in pregnancy with the use of prospective, serial objective measures.
In summary, although data are emerging that suggest an association between SDB and adverse pregnancy outcomes, including preeclampsia and GDM, current evidence is limited and mostly correlational. Therefore, a substudy to the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-be (nuMoM2b), a study of adverse outcomes in pregnant nulliparous women, was undertaken to estimate the prevalence of and characteristics of SDB among women during pregnancy and to determine whether SDB is a risk factor for adverse pregnancy outcomes. Serial, objective assessments of SDB across pregnancy were performed. This article reports on the methods that were developed to obtain high-quality sleep data across multiple sites in pregnant women.
Methods
The nuMoM2b parent study
The design of the nuMoM2b parent study is presented in detail elsewhere. The nuMoM2b study enrolled 10,037 women between October, 2010, and September, 2013. The study which was managed by a Data Coordinating and Analysis Center at RTI International was conducted at 8 clinical sites: Case Western Reserve University, Columbia University, Indiana University, University of Pittsburgh, Northwestern University, University of California at Irvine, University of Pennsylvania, and the University of Utah. Inclusion criteria for the parent study were nulliparity (no previous delivery at ≥20 weeks’ gestational age), a viable singleton pregnancy with estimated gestational age between 6 0 –13 6 weeks, and intention to deliver at a participating clinical site hospital. Exclusion criteria included age <13 years, a history of ≥3 pregnancy losses, donor oocyte pregnancy, planned pregnancy termination, malformations likely to be lethal and aneuploidies known at or before enrollment, previous enrollment, and inability to provide informed consent.
Study visits were conducted at 4 time points (visits 1-4: 6 0 –13 6 , 16 0 –21 6 , 22 0 –29 6 weeks’ gestation) and at the time of delivery. Data were collected through interviews, self-administered questionnaires, clinical measurements (that included height, weight, and neck circumference), ultrasound scans, and medical records review to ensure collection of pertinent demographic, psychosocial, dietary, physiologic, and pregnancy outcome information. In addition, maternal serum, plasma, urine, and cervicovaginal fluid were collected at each visit (1, 2, and 3); maternal blood for DNA was collected at visit 1, and maternal serum and plasma, cord blood plasma and placenta were collected at delivery. These samples were aliquoted and stored in a repository for later use.
All subjects who were enrolled in the nuMoM2b parent study were asked to complete a comprehensive sleep questionnaire at the first and third study visit. These included questions regarding the timing of sleep and sleep duration, work schedules (eg, shift work, night work), sleep positions, previously diagnosed sleep disorders, and questions from the following commonly used sleep questionnaires: (1) the Berlin Questionnaire (a screening instrument designed to identify adults likely to have OSA through a series of questions pertaining to snoring behavior and wake-time sleepiness), (2) the Epworth Sleepiness Scale (provides a measurement of daytime sleep propensity that uses estimates of the likelihood of dozing off or falling asleep in 8 different sedentary situations), (3) the International Restless Legs Syndrome Study Group diagnostic criteria for restless legs syndrome, and (4) the Women’s Health Initiative Insomnia Rating Scale (quantifies insomnia symptom severity).
Aims and hypotheses
The nuMoM2b-SDB substudy was designed and powered to test the primary hypothesis that SDB that occurs early and/or appears late in pregnancy is associated with an increased incidence of preeclampsia. The secondary aims were to (1) examine the association between SDB in pregnancy and GH and GDM, (2) determine the prevalence of objectively measured SDB in early and late pregnancy, (3) delineate characteristics (ie, risk profile) of women who exhibit SDB in early and late pregnancy, and (4) define the SDB subtypes (eg, AHI threshold, degree of nocturnal hypoxemia) in pregnancy that are associated most strongly with maternal cardiovascular and metabolic disease (preeclampsia, GH, GDM).
Exploratory aims were to evaluate SDB as a risk indicator for altered fetal growth and preterm birth (spontaneous and iatrogenic). Sleep questionnaire data, obtained as part of the parent study, will be used to examine the association between self-reported measures of sleep deficiency (eg, sleep duration, timing, quality), sleep disorder symptoms (eg, snoring, insomnia, restless legs), daytime function (eg, daytime sleepiness), physician-diagnosed sleep disorders, and the incidence of adverse pregnancy outcomes (eg, preeclampsia, GH, GDM). Data from objective SDB assessments will be used to examine the sensitivity and specificity of self-reported SDB symptoms (eg, snoring, gasping for air, daytime sleepiness), to determine the clinical utility of SDB symptom evaluation in pregnancy.
Design
The nuMoM2b-SDB substudy enrolled 3702 nuMoM2b participants between March, 2011, and September, 2013. The inclusion criterion was enrollment in the parent study. Women who were excluded from the SDB substudy had the following conditions: current continuous positive airway pressure (CPAP) treatment for SDB, severe asthma that required continuous oral steroid therapy for >14 days, and conditions that required oxygen supplementation. Eligible women were approached for enrollment at the first nuMoM2b parent study visit. A trained study coordinator obtained written informed consent (and written assent for minors). Institutional review board approval was obtained at all sites.
Home sleep testing was performed with the Embletta-Gold device (Embla Systems, Broomfield, CO; Figure 1 ) and was self-administered by the participant after nuMoM2b parent study visits 1 and 3. The pocket-sized device contains 4 recommended and validated sensors for measuring SDB parameters: a nasal pressure transducer (that measures nasal airflow and waveform, which are needed for the detection of apneas and hypopneas and airflow limitation), thoracic and abdominal inductance plethysmography bands (XactTrace belts; Embla Systems) that measure respiratory effort for distinguishing central from obstructive apneas and as a back-up for the nasal pressure signal), and finger pulse oximetry (to quantify the level and duration of oxygen desaturation). In addition, bipolar electrocardiogram results and body position were recorded.
The participant was instructed on the proper placement of the various Embletta-Gold device sensors during the study visits by trained and certified site staff. In particular, participants were instructed on how to place the thoracic and abdominal inductance plethysmography bands on their gravid abdomen ( Figure 1 ). Application of sensors was demonstrated by the staff, and participants were then asked to apply them to demonstrate their understanding. Participants were instructed to apply the device before bed within 48 hours of the study visit while following a routine sleep schedule. They were provided instruction sheets and a staff phone number to use if questions arose during application or monitoring. Arrangements were made to retrieve the monitor (eg, drop off, by prepaid mailer). The participant was also asked to complete a brief survey regarding her experience with the device after completion of each in-home sleep study. Once the device was returned, the sleep study data were downloaded at the clinical site and electronically transmitted to the Sleep Reading Center (Brigham and Women’s Hospital, Boston, MA) by a secured interface.
All participants were given an educational pamphlet on enrollment in the study. This pamphlet contained a general description of the importance of healthy sleep. The pamphlet stressed how insufficient sleep and excessive sleepiness can affect daytime function adversely, especially driving, and urged participants who were concerned about these symptoms to seek medical attention.
Pregnancy outcome data were collected by chart abstraction as described in the parent study methods paper. Specifically, for any participant with documented hypertension, which was defined as systolic blood pressure ≥140 mm Hg or diastolic blood pressure ≥90 mm Hg on 2 occasions at least 6 hours apart or on 1 occasion followed by antihypertensive medication therapy, a detail chart review was required that included assessment of blood pressure severity, new-onset cerebral and visual disturbances, epigastric pain or pulmonary edema, proteinuria, platelet and hemoglobin values, liver enzyme level, and creatinine level. Preeclampsia and GH will be analyzed with the use of both the 2002 and the updated 2013 American College of Obstetricians and Gynecologists criteria.
Scoring and quality control
Quality control of data collection and analysis was established through several levels of training, certification, and ongoing monitoring that was overseen by the central Sleep Reading Center. Detailed descriptions of the nuMoM2b-SDB substudy responsibilities at the clinical sites and the Sleep Reading Center, training and certification requirements, and quality control and quality assurance procedures are given in the Appendix . Many of the study materials are also provided in the Appendix ( Supplementary Materials , Appendix 4 ). The scoring methods were adapted from the Sleep Heart Health Study, which is available through the National Sleep Research Resource web portal ( sleepdata.org ). Before beginning data collection, key staff attended a central training session at which the scientific objectives of the study, the protocol and manual of operations, technical information on the use of the Embletta-Gold device, and study software were reviewed. Most study staff had limited-to-no previous experience with sleep testing. Staff members were required to become certified to administer home sleep testing by completing written and practical examinations on the study protocol and procedures and successfully administering and transmitting a high-quality practice home sleep test to the Sleep Reading Center.
Maintenance of certification required transmission of at least one successful sleep study per month, except towards the end of study period at which time sleep test volume was declining, then maintenance of certification was adjudicated by the Sleep Reading Center. Technicians at the Sleep Reading Center were also trained and certified on sleep study scoring and analysis by showing evidence of 95% agreement with respiratory event identification in a test set of sleep studies. Technician performance was monitored over time with repeated scoring of test and practice sets to identify within and between scorer variations.
On receipt at the Sleep Reading Center, each study was examined to determine whether it met minimal criteria for acceptance (minimal of 2 hours of artifact-free oximetry data plus concurrent signals from at least one breathing sensor); urgent referrals and quality grades were assigned. Each channel was graded as to the period of artifact-free data, with an overall study grade assigned based on the absolute duration of artifact-free data for the nasal pressure cannula, oximeter, and each respiratory effort band.
Level 3 sleep monitoring devices, such as used in this study, do not record sleep directly (ie, with electroencephalography and electromyography signals). Therefore, sleep onset and offset and periods of prolonged wakefulness are identified by certified polysomnologists who use the information from both participant-completed questionnaires on bed and wake times and the visualized patterns of heart rate, breathing pattern, movement, and artifact. The sleep period is defined as the period between sleep onsets and offsets. Sleep onset is identified based on self-reported bedtime plus visualization of reduced signal artifact, decreased heart rate, regularization of breathing pattern, and stability of the position sensor (which indicates a supine or lateral position). Conversely, sleep offset is identified by evidence of sustained movement artifact, changing position, increase in heart rate, and participant-reported wake time. After the initiation of sleep, segments of the study were excluded from analysis if significant movement or artifact occurred for a period of ≥20 minutes.
The Embletta-Gold recordings were scored to quantify the types and number of SDB events that occurred during the estimated sleep period with the use of the following definitions : (1) obstructive apnea ( Figure 2 , A): amplitude (peak to trough) of the nasal pressure signal flat for ≥10 seconds and accompanied by effort on either respiratory band; (2) central apnea ( Figure 2 , B): amplitude (peak to trough) of the nasal pressure signal flat for ≥10 seconds and accompanied by complete absence of effort on both respiratory bands; (3) 2 classes of hypopneas ( Figure 2 , C): scored on the basis of alternative amplitude reduction criteria: (a) based on ≥30% or (b) ≥50% reduction of amplitude in the nasal pressure signal or the respiratory sum channel (if nasal pressure signal is not present) for ≥10 seconds duration (hypopnea events were annotated regardless of associated desaturation and later linked with oxygen saturation values with the use of customized software so that apnea-hypopnea indices could be derived with the use of a flexible range of criteria [eg, ≥3% or ≥4% desaturation]); and (4) AHI : recorded according to the total number of apneas and hypopneas per hour of estimated sleep.
Blinding and urgent alerts
Currently, there are no sanctioned pregnancy-specific guidelines for SDB treatment, no data on which to base fetal or maternal parameters for treatment, and no evidence that treatment in the short term impacts maternal or neonatal outcomes. Because SDB may fluctuate particularly during pregnancy, it is also important to interpret the clinical significance of any single assessment of SDB cautiously. Therefore, given the limited available data, clinical equipoise surrounds the issue of SDB in pregnancy, and participants and care providers were blinded to the sleep study results, unless the Sleep Reading Center identified a study meeting “urgent alert” criteria. Sleep studies that showed an AHI of >50 or severe hypoxemia (oxygen saturation of <90% for >10% of the estimated sleep time) were identified as urgent alert studies. These studies were reviewed by a Sleep Reading Center physician and reported to the clinical site and the Data Coordinating and Analysis Center within 14 days of study receipt. Other findings that triggered an urgent referral included baseline oxygen saturation (before sleep onset) of <88%; heart rate for >2 continuous minutes that were <40 or >150 beats per minute; the presence of a sustained wide complex rhythm (≥3 consecutive beats) awake or asleep, and type 2 second-degree and third-degree atrioventricular heart block.
The site physician reviewed all urgent findings and identified appropriate resources for referral for the participant. The participant’s obstetric care provider was then notified of the results by phone and by letter so that arrangements for timely referral for full evaluation could be made. Similar urgent referral criteria have been used in several other large population based studies of SDB (eg, The Sleep Health Heart Study ).
Power and sample size
A target sample size of 3630 women was selected to ensure that there would be sufficient numbers of women with SDB in either early or late pregnancy to provide adequate power for assessment of the association between maternal SDB and preeclampsia. The calculations took into account a sleep study failure rate (which allowed for a single attempted retest) of 9% of the participants, based on the previous experience of the Sleep Reading Center with the Embletta unit; a 10% study dropout/loss to follow up, and a conservative assumption of 25% refusal to repeat the sleep study in the third trimester. Also, it was assumed that 3630 women would yield approximately 180 women (5%) with SDB (AHI of ≥5) in early pregnancy and 360 women (10%) in late pregnancy. With these assumptions and setting the type I error at 2-sided α = .05, the target sample size yielded at least 80% power to detect a relative risk of 2.0 (1.8) for preeclampsia for women with SDB in early (late) pregnancy, with the assumption of a 7% incidence of preeclampsia among women without SDB. Analysis of more common outcomes (eg, growth restriction defined as birthweight <10th percentile for gestational age, preterm birth <37 weeks of gestation) will have >80% power for similar effect sizes.
Results
A total of 3702 women who were enrolled to nuMoM2b attempted to complete an objective sleep breathing assessment during the study. Table 1 gives the number of objective (home sleep test) and subjective (the questionnaire data) sleep assessments that were completed on this subcohort. Objective data were obtained at visit 1 on 3261 women, which was 88.1% of studies attempted, and at visit 3 on 2511 women, which was 87.6% of studies attempted. Across visits, objective data were obtained on 5581 of 6567 sleep studies (85.0%) in the first attempt. For the remaining 986 sleep studies, a second attempt was made on 224 women, and objective data were obtained on 191 (85%). There was little change in the failure rate over the course of data collection. The most common reasons for failed studies were (1) failure of the participant to wear the equipment (n = 244 studies; 30.7%), (2) <2 hours of oximetry (n = 240 studies; 30.2%), and (3) equipment problems (n = 200 studies; 25.2%). For the studies for which objective data were obtained, a breakdown on the signal quality for electrocardiogram, cannula flow, the thoracic effort band, the abdominal effort band, and oximetry is provided in Table 2 . It should be noted that oximetry of at least 2 hours was required to score the study. All women in the nuMoM2b parent study were asked to complete a subjective sleep questionnaire. It was obtained on 2996 of the 3261 women with objective data at visit 1 and on 2454 of the 2511 women with objective data at visit 3. The objective measures for both visits 1 and 3 were available for 2336 women, and objective and subjective measures were available on 2152 women.
| Characteristic | n (%) |
|---|---|
| Visit 1 | |
| Objective assessment attempted | 3701 |
| Objective data obtained | 3261 (88.1) |
| Subjective data obtained | 3372 (91.1) |
| Objective and subjective data available | 2996 (81.0) |
| Visit 3 | |
| Objective assessment attempted | 2866 |
| Objective data obtained | 2511 (87.6) |
| Subjective data obtained | 2780 (97.0) |
| Objective and subjective data available | 2454 (85.6) |
| Both visits | |
| Objective assessment attempted | 2865 |
| Objective data obtained | 2336 (81.5) |
| Subjective data obtained | 2603 (90.9) |
| Objective and subjective data available | 2152 (75.1) |
a The 3702 women who were enrolled to Nulliparous Pregnancy Outcomes Study Monitoring Mothers-to-be had at least 1 objective sleep disordered breathing assessment; in one case, the woman decided against the sleep assessment at visit 1 but took the assessment at visit 3.
| Artifact-free data a | EKG, n (%) | Cannula flow, n (%) | Effort band, n (%) | Oximetry, n (%) | |
|---|---|---|---|---|---|
| Thoracic | Abdominal | ||||
| Visit 1, % | |||||
| <25 | 35 (1.1) | 203 (6.2) | 512 (15.7) | 500 (15.3) | 0 |
| 25-49 | 18 (0.6) | 183 (5.6) | 64 (2.0) | 46 (1.4) | 0 |
| 50-74 | 42 (1.3) | 382 (11.7) | 154 (4.7) | 97 (3.0) | 32 (1.0) |
| 75-94 | 344 (10.5) | 575 (17.6) | 579 (17.8) | 353 (10.8) | 174 (5.3) |
| ≥95 | 2822 (86.5) | 1918 (58.8) | 1952 (59.9) | 2265 (69.5) | 3055 (93.7) |
| Total | 3261 (100.0) | 3261 (100.0) | 3261 (100.0) | 3261 (100.0) | 3261 (100.0) |
| Visit 3, % | |||||
| <25 | 23 ( 0.9) | 186 (7.4) | 388 (15.5) | 401 (16.0) | 0 |
| 25-49 | 14 (0.6) | 159 (6.3) | 32 (1.3) | 60 (2.4) | 0 |
| 50-74 | 31 (1.2) | 279 (11.1) | 113 (4.5) | 70 (2.8) | 18 (0.7) |
| 75-94 | 280 (11.2) | 449 (17.9) | 482 (19.2) | 265 (10.6) | 106 (4.2) |
| ≥95 | 2163 (86.1) | 1438 (57.3) | 1496 (59.6) | 1715 (68.3) | 2387 (95.1) |
| Total | 2511 (100.0) | 2511 (100.0) | 2511 (100.0) | 2511 (100.0) | 2511 (100.0) |
| All visits, % | |||||
| <25 | 58 (1.0) | 389 (6.7) | 900 (15.6) | 901 (15.6) | 0 |
| 25-49 | 32 (0.6) | 342 (5.9) | 96 (1.7) | 106 (1.8) | 0 |
| 50-74 | 73 (1.3) | 661 (11.5) | 267 (4.6) | 167 (2.9) | 50 (0.9) |
| 75-94 | 624 (10.8) | 1024 (17.7) | 1061 (18.4) | 618 (10.7) | 280 (4.9) |
| ≥95 | 4985 (86.4) | 3356 (58.1) | 3448 (59.7) | 3980 (69.0) | 5442 (94.3) |
| Total | 5772 (100.0) | 5772 (100.0) | 5772 (100.0) | 5772 (100.0) | 5772 (100.0) |
a Percentage of artifact-free data based on estimated sleep time.
Demographic characteristics of the 3702 women are presented in Table 3 . The mean age of the women at entry into the study was 26.7 years (±5.6 years). Sixty percent (59.6%) of the women were non-Hispanic white; 14.1% of the women were non-Hispanic black; 17.7% of the women were Hispanic; 3.6% of the women were Asian, and 5% of the women were classified as “other” on race/ethnicity. In 49.0% of the women, their prepregnancy BMI would classify them as normal weight (BMI, 18.5-24.9 kg/m 2 ), 25.4% as overweight (BMI, 25.0-29.9 kg/m 2 ), 23.4% as obese or morbidly obese (BMI, ≥30 kg/m 2 ), and 2.3% as underweight (BMI, <18.5 kg/m 2 ). Eighteen percent of the participants (18.1%) smoked during the 3 months before the pregnancy, and 6.4% of them smoked in the month before the first study visit. Sixty percent of the women (59.4%) were 12-13 weeks’ gestation at screening.
| Characteristic (N = 3702) | Statistic |
|---|---|
| Maternal age, y | |
| Mean ± SD | 26.7 ± 5.6 |
| Median (interquartile range) | 27.0 (22–31) |
| Category, n (%) | |
| 13-21 | 801 (21.6) |
| 22-35 | 2659 (71.8) |
| >35 | 242 (6.5) |
| Maternal race/ethnicity, n (%) | |
| Non-Hispanic white | 2208 (59.6) |
| Non-Hispanic black | 523 (14.1) |
| Hispanic | 654 (17.7) |
| Asian | 133 (3.6) |
| Other | 184 (5.0) |
| Maternal education status, n (%) | |
| Less than high school | 270 (7.3) |
| Completed high school or general education diploma | 478 (12.9) |
| Some college | 787 (21.3) |
| Associate or technical degree | 403 (10.9) |
| Completed college | 1014 (27.4) |
| Degree work beyond college | 750 (20.3) |
| Income and size of household relative to Federal poverty level, n (%) | |
| >200% | 1975 (67.1) |
| 100-200% | 483 (16.4) |
| <100% | 487 (16.5) |
| Method of paying for healthcare, n (%) a | |
| Government insurance | 1070 (29.1) |
| Military insurance | 34 (0.9) |
| Commercial health insurance | 2495 (67.8) |
| Personal household income | 602 (16.4) |
| Other | 50 (1.4) |
| Prepregnancy body mass index, n (%) | |
| Underweight (<18.5 kg/m 2 ) | 83 (2.3) |
| Normal weight (18.5-24.9 kg/m 2 ) | 1783 (49.0) |
| Overweight (25.0-29.9 kg/m 2 ) | 922 (25.4) |
| Obese (30.0-34.9 kg/m 2 ) | 440 (12.1) |
| Morbidly obese (>35 kg/m 2 ) | 409 (11.3) |
| Smoking, n (%) | |
| Ever smoked | 1503 (40.6) |
| Smoked during 3 months before pregnancy | 671 (18.1) |
| Among smokers during 3 months before pregnancy, cigarettes per day | |
| <20 | 573 (85.7) |
| 20-40 | 95 (14.2) |
| >40 | 1 (0.2) |
| Estimated gestational age at screening, n (%) | |
| <8 wk 0 d | 69 (1.9) |
| 8 wk 0 d to 9 wk 6 d | 396 (10.7) |
| 10 wk 0 d to 11 wk 6 d | 1039 (28.1) |
| 12 wk 0 d to 13 wk 6 d | 2198 (59.4) |
a Percentages do not add up to 100% because participants were allowed to select multiple methods of payment for health care.
Results
A total of 3702 women who were enrolled to nuMoM2b attempted to complete an objective sleep breathing assessment during the study. Table 1 gives the number of objective (home sleep test) and subjective (the questionnaire data) sleep assessments that were completed on this subcohort. Objective data were obtained at visit 1 on 3261 women, which was 88.1% of studies attempted, and at visit 3 on 2511 women, which was 87.6% of studies attempted. Across visits, objective data were obtained on 5581 of 6567 sleep studies (85.0%) in the first attempt. For the remaining 986 sleep studies, a second attempt was made on 224 women, and objective data were obtained on 191 (85%). There was little change in the failure rate over the course of data collection. The most common reasons for failed studies were (1) failure of the participant to wear the equipment (n = 244 studies; 30.7%), (2) <2 hours of oximetry (n = 240 studies; 30.2%), and (3) equipment problems (n = 200 studies; 25.2%). For the studies for which objective data were obtained, a breakdown on the signal quality for electrocardiogram, cannula flow, the thoracic effort band, the abdominal effort band, and oximetry is provided in Table 2 . It should be noted that oximetry of at least 2 hours was required to score the study. All women in the nuMoM2b parent study were asked to complete a subjective sleep questionnaire. It was obtained on 2996 of the 3261 women with objective data at visit 1 and on 2454 of the 2511 women with objective data at visit 3. The objective measures for both visits 1 and 3 were available for 2336 women, and objective and subjective measures were available on 2152 women.
