Material and Methods
This prospective single-center study took place at the Lille University
Hospital Center, at the Jeanne de Flandre maternity ward, and included a
population of obese pregnant women who were offered overnight
in-hospital polysomnography for OSA screening. The Lille Hospital Ethics
Committee approved this study (CPP 09/65 N° 2009-A01018-49).
Its principal objective was to
study the prevalence of OSA in the population of obese women receiving
prenatal care and giving birth at our hospital, specifically those with
a prepregnancy BMI >35 kg/m². The first of our secondary
objectives was to compare the course of pregnancy in women with and
without OSA, especially for the onset of pregnancy-related vascular
disorders (pregnancy-related hypertension, preeclampsia, eclampsia,
HELLP syndrome, or fetal growth restriction, FGR), but also for their
pregnancy outcome (type of delivery and newborn’s characteristics). The
last secondary objective was to examine whether various criteria,
including maternal age, parity, BMI, history of chronic hypertension,
history of diabetes, family history of OSA, weight gain during
pregnancy, and gestational diabetes might be risk factors for developing
OSA in this population.
Participation in the study was offered to all pregnant women aged at
least 18 years receiving prenatal care at the Jeanne de Flandre
maternity ward with a prepregnancy BMI >35 kg/m². The
polysomnography had to take place after 24 and before 32 weeks of
gestation. Women were excluded if they refused to participate, did not
sign the informed consent, had a twin or higher-order multiple
pregnancy, had a guardian or conservator, or took medication likely to
modify OSA. Obstetricians explained the study to women meeting the
inclusion criteria in a special consultation and gave them written
information about it. After time to consider participation, the women
who agreed provided written informed consent before inclusion.
These women were then followed up monthly from the fourth month of
pregnancy, during prenatal consultations, when obstetric data were
collected. Fetal monitoring took place by monthly ultrasound to evaluate
fetal weight and by fetal and uterine artery Doppler scans.
Polysomnography took place between 24 and 32 weeks of gestation. Mode of
delivery and neonatal status were recorded at birth.
The following obstetric data were collected during pregnancy: maternal
age, parity, prepregnancy BMI, type 1 or 2 diabetes, chronic
hypertension, history of phlebitis and/or pulmonary embolism, family
member with OSA, gestational diabetes, weight gain during pregnancy,
hospitalization during pregnancy, and presence of any pregnancy-related
vascular disease or complication (pregnancy-related hypertension,
preeclampsia, eclampsia, HELLP syndrome, or FGR). These
pregnancy-related vascular diseases were grouped together as a composite
criterion. The criteria for their diagnosis were those defined by the
French national guidelines.21
Polysomnography was performed during one night of hospitalization in the
hospital’s sleep laboratory, recording an electroencephalogram,
electro-oculograms, submental and bilateral anterior tibialis
electromyography, an electrocardiogram, nasal and oral air-flow, oxygen
saturation and thoracic and abdominal movement. Various clinical
indicators were also collected to assess the existence of OSA
(ronchopathy or snoring, respiratory pauses, nocturia, night sweats,
morning headaches, perception of nonrestorative sleep, and excessive
daytime somnolence). Analysis of these clinical and polysomnographic
data enabled us to define two groups of women: one group with OSA and
one without it. AHI ≥5 measured by polysomnography defined OSA. Among
the women with OSA, we distinguished those with mild or moderate sleep
apnea (AHI <30) and those with severe OSA (AHI ≥30). Severity
was also assessed by simultaneous measurement of arterial oxygen
desaturation and consideration of the complete clinical picture
(hypersomnolence, neuropsychological disorders, and hypertension).
Ventilation by continuous positive airway pressure (CPAP) was proposed
to the women with severe OSA, with continuing medical follow-up at the
sleep center.
Data about delivery and the baby were collected postpartum: mode of
delivery, spontaneous or induced labor, term at delivery, birth weight,
acid-base status, and NICU
transfer.
The sample size was calculated on the basis of the estimated 95%
confidence interval (95% CI) of the theoretical frequency of women with
a BMI >35 and OSA (that is, the principal study objective).
This 95% CI was calculated with Sachs’ method, and the sample size was
calculated to obtain a given level of precision for this CI, defined as
half of it. By using the standard formula, which can determine positive
predictive value from sensitivity, specificity, and prevalence, we were
able to estimate the frequency of OSA in women with a BMI
>35 kg/m2 at 56%. We set the precision
at 12.5% (length of CI: 25%). In these conditions, we calculated that
68 women were necessary for the study (theoretical frequency estimated
at 43.3–68.2%).22The frequency of OSA was
estimated by its 95% CI. For the descriptive data analysis, the
qualitative data were presented as numbers and percentages, and the
quantitative data as means and their standard deviations. The normality
of the numeric parameters was verified graphically and by the
Shapiro-Wilk test. The groups with and without OSA were compared by
Chi-square or Fisher’s exact tests for the qualitative variables (e.g.,
age, BMI, weight gain, birth weight, Apgar score) and by the Kruskal
Wallis or Mann-Whitney tests for the quantitative variables (e.g.,
chronic hypertension, diabetes, the vascular disease composite
criterion). Significance was set at 5%. The analysis was performed with
SAS software (version 9.4, SAS Institute, Cary, NC).