Maternal oxygenation during normal labour

Arterial oxyhaemoglobin saturation (SaO2) was monitored continuously during normal labour in 33 healthy parturients receiving pethidine and nitrous oxide for analgesia. Sixteen (49%) had episodes exceeding 10 s duration when SaO2 was less than 90% (mean 83.7%, range 89-60%). Two women had multiple episodes of profound hypoxia with SaO2 less than 70%.