Obstructive Sleep Apnea in Pregnancy: Development of a Pregnancy-Specific Screening Tool
Conditions: Sleep Apnea, Obstructive, Pregnancy, Obesity, Morbid
Sponsor: Duke University

 
 
 
 
 
Obstructive Sleep Apnea in Pregnancy:  
Development of a Pregnancy-Specific Screening Tool 
 
NCT02383706 
 
Document Date: August 1, 2018 
 

This study was approved by the Duke University Medical System Institutional 
Review Board and registered in ClinicalTrials.gov (NCT02383706). We prospectively 
enrolled adult pregnant, nulliparous and multiparous subjects, between 24 and 35 
weeks gestation from a university-affiliated prenatal clinic. Women were included if they 
had a BMI > 40 kg.m-2 at the time of enrollment and were 18 years or older. The World 
Health Organization classification of obesity was utilized to define class 3 (extreme) 
obesity.1 Women with an established diagnosis of OSA or chronic opiate use, and 
subjects who did not speak English were excluded.  
Following informed consent, demographic data was recorded (including pre-
pregnancy BMI from chart review) and subjects completed three sleep disordered 
breathing screening questionnaires: the Berlin2 (BQ) and STOP-BANG3,4 
questionnaires, and the American Society of Anesthesiologists’ (ASA) checklist.5 
Subjects also completed the Epworth Sleepiness Scale (ESS) which is used to assess 
sleepiness that can be associated with OSA.6 An OSA risk score was also calculated for 
each subject using the method proposed for use in pregnant women by Facco et al.2  
OSA risk score = Age + BMI pre-pregnancy + 15 (if frequent snoring) + 15 (if chronic hypertension) 
The BQ, STOP-BANG, and ASA questionnaires, as well as the ESS were scored 
using published methods.2,5-7 The BQ contains 10 items classified into three categories: 
Category 1 concerns snoring; Category 2 concerns daytime sleepiness; and Category 3 
relates to BMI > 30 kg.m-2 and chronic hypertension. The BQ is considered high risk for 
OSA if two of three categories were scored as positive.2 Similarly, the ASA checklist 
contains 12-items in three categories: clinical signs and symptoms; history of apparent 
airway obstruction during sleep; and somnolence. If 2 or more of these categories are 

endorsed, the patient is considered at high risk for OSA.5 Each item on the STOP-
BANG questionnaire receives one point, with the highest total possible score in this 
cohort equal to 6 (as male gender and age greater than 50 years do not apply to any of 
the subjects).7,8 The ESS is considered concerning for excessive daytime sleepiness if 
scores are in the 11-24 range.6 
 
Study data were entered into and managed using REDCap electronic data 
capture tools hosted at Duke University. REDCap (Research Electronic Data Capture) 
is a secure, web-based application designed to support data capture for research 
studies, providing: 1) an intuitive interface for validated data entry; 2) audit trails for 
tracking data manipulation and export procedures; 3) automated export procedures for 
seamless data downloads to common statistical packages; and 4) procedures for 
importing data from external sources.9 
 
Vital signs were recorded, and subjects underwent a physical examination of the 
neck and upper airway by trained research assistants in the Department of 
Anesthesiology to measure neck circumference4 and thyromental distance, and to 
assess retrognathia, tongue scalloping10, Mallampati score (MMS)11, modified MMS12, 
tonsil size and lateral pharyngeal wall narrowing. MMS is a 1-4 numerical rating system 
commonly used to assess the airway and predict difficulty of intubation that is assessed 
by asking the subject to open their mouth as wide as possible with the tongue 
protruding. The modified Mallampati score leaves the tongue inside the mouth. Neck 
circumference was measured using a disposable measuring tape at the midpoint of the 

neck just below the thyroid cartilage. Thyromental distance was measured using a 
disposable paper measuring tape from the mandible to the top of the thyroid cartilage. 
Retrognathia, tongue scalloping, MMS, modified MMS, tonsil size and lateral 
pharyngeal wall narrowing were rated using an illustrated numerical scoring tool. 
 
Subjects received an unattended type III home sleep apnea test (ApneaLink 
Air, ResMed, Poway, CA, USA), and instructions for wearing it during one night of 
sleep. The home sleep test consists of a pulse oximeter for recording of oxygen 
saturation and heart rate, a respiratory effort belt for measurement of respiratory effort, 
and a nasal sensor for detection of flow limitation, apnea hypopnea index (AHI) and 
snoring. The software on the device calculates AHI from the sum average number of 
apneas (80%-100% reduction in airflow with respiratory effort > 10 seconds) and 
hypopneas (50%-80% reduction in airflow with respiratory effort > 10 seconds) per hour 
during the recording time, based on the standard definitions of the American Academy 
of Sleep Medicine. The software also generates a report with details regarding variation 
in oxygen saturation during the study. Subjects with an AHI greater than 5 per hour on 
the home sleep test were referred to a sleep medicine physician for further evaluation.     
 
Pregnancy outcomes were followed for all subjects, including maternal death, 
gestational diabetes, cerebrovascular accident, spontaneous labor, induction of labor, 
oxytocin administration during labor, cesarean delivery, estimated blood loss, neonatal 
weight, and composite outcomes of adverse maternal cardiovascular and peripartum 
events, and adverse fetal outcomes. A composite adverse maternal cardiovascular 

outcome combined cases of: gestational hypertension; mild and severe preeclampsia; 
eclampsia; cardiomyopathy; and congestive heart failure. A composite adverse 
peripartum outcome included cases of: postpartum hemorrhage; maternal ICU 
admission; and post-operative wound infections. A composite adverse fetal outcome 
included cases of: neonatal intensive care unit admission; fetal growth restriction; 
preterm delivery (< 37 weeks gestation); and fetal demise. 
 
Statistical analysis 
OSA outcome was defined as AHI ≥ 5 events per hour among patients with at 
least 2 hours of nasal air flow time recorded. This measure was chosen to assess 
outcome because it represents the threshold for referral for in laboratory PSG and an 
OSA screening measure will need to be able to sensitively and specifically indicate 
when a referral for PSG is needed. We summarized the patient demographic, physical, 
and clinical characteristics as well as questionnaire responses in each outcome group 
via mean (SD) or median (Q1, Q3) for numeric variables and N (%) for categorical 
variables. We assessed univariate associations of patient characteristics and 
questionnaire responses with OSA outcome via t-test or Wilcoxon rank sum test for 
numeric variables, and chi-square or Fisher exact test for categorical variables. 
 
We assessed the performance and agreement of the previously defined OSA risk 
scores via receiver operating curve (ROC) area under the curve (AUC) analysis, logistic 
regression, and Kendall Tau correlation for the numeric scores, and via sensitivity and 

specificity, net reclassification indices (NRI) and Kappa statistics for the binary risk 
stratification. 
 
We designed the study with an expectation of an OSA positive rate of 30-40% in 
our high-risk population.1,2 A study of 80 patients (24-32 with OSA) with completed valid 
home sleep test, achieves 79% power in a logistic regression with two-sided alpha=0.05 
to detect an odds ratio of 2.5 for a numeric risk score when the OSA rate is 35%. For 
the Kappa statistic used to assess agreement, with 80 subjects and an OSA rate of 
35%, we will achieve 82% power at alpha = 0.05 to detect the difference between a 
kappa of 0.45 (fair agreement) and 0.75 (strong agreement). Power and sample size 
calculation were performed in NQuery (Statistical Solutions Ltd) software, statistical 
analysis was performed in SAS v9.4 (SAS Inc., Cary, NC), and significance was set at 
0.05 level. 
 
 
 
 
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