Upper-airway flow limitation and transcutaneous carbon dioxide during sleep in normal pregnancy

Sleep during pregnancy involves a physiological challenge to provide sufficient gas exchange to the fetus. Enhanced ventilatory responses to hypercapnia and hypoxia may protect from deficient gas exchange, but sleep-disordered breathing (SDB) may predispose to adverse events. The aim of this study was to analyze sleep and breathing in healthy pregnant women compared to non-pregnant controls, with a focus on CO₂ changes and upper-airway flow limitation.

Healthy women in the third trimester and healthy non-pregnant women with normal body mass index (BMI) were recruited for polysomnography. Conventional analysis of sleep and breathing was performed. Transcutaneous carbon dioxide (TcCO₂) was determined for each sleep stage. Flow-limitation was analyzed using the flattening index and TcCO₂ values were recorded for every inspiration.

Eighteen pregnant women and 12 controls were studied. Pregnancy was associated with shorter sleep duration and more superficial sleep. Apnea-hypopnea index, arterial oxyhemoglobin desaturation, flow-limitation, snoring or periodic leg movements were similar in the two groups. Mean SaO₂ and minimum SaO₂ were lower and average heart rate was higher in the pregnant group. TcCO₂ levels did not differ between groups but variance of TcCO₂ was smaller in pregnant women during non-rapid eye movement (NREM). TcCO₂ profiles showed transient TcCO₂ peaks, which seem specific to pregnancy.

Healthy pregnancy does not predispose to SDB. Enhanced ventilatory control manifests as narrowing threshold of TcCO₂ between wakefulness and sleep. Pregnant women have a tendency for rapid CO₂ increases during sleep which might have harmful consequences if not properly compensated.