Nocturnal hypoxaemia in late pregnancy.

We have measured arterial oxygen saturation (SpO2) continuously overnight in 13 non-pregnant (NP), 13 pregnant normotensive (NPIH) and 15 pregnant patients with a diagnosis of pregnancy-induced hypertension (PIH). The two pregnant groups did not differ in duration of pregnancy (> 35 weeks) and none was in labour. There was no significant difference in age between these three groups. Mean SpO2 in group NP was 98.5% (range 97-99%). This was significantly higher than that in group NPIH (95.2 (91-98) %) and group PIH (94.9 (89-99) %). In seven pregnant patients, more than 20% of the recording was spent with an SpO2 < 90%. We conclude that a significant number of pregnant women (> 35 weeks' gestation) suffer from prolonged nocturnal hypoxaemia.