Chronobiology of labour pain perception: an observational study

Circadian variation may affect many biological and pharmacological phenomena. To assess circadian variations in labour pain perception, 222 consecutive nulliparous women with uncomplicated pregnancy, spontaneous labour, cervical dilatation (3–5 cm), ruptured membranes and normal fetal heart rate tracings were studied. Visual analogue pain scores (VAPS) were analysed and divided into four periods: night (1:01 a.m. to 7:00 a.m.), morning (7:01 a.m. to 1:00 p.m.), afternoon (1:01 p.m. to 7:00 p.m.) and evening (7:01 p.m. to 1:00 a.m.). VAPS were also compared between daytime (morning+afternoon) and nocturnal (evening+night) periods. Daytime mean VAPS were lower than nocturnal scores [75.6 (15.1) vs 85.7 (14.1), P