['As a first step towards evaluating the role of oxidative stress in the process of labour, we tested whether term labour is associated with increased oxidisibility of maternal serum lipids.', 'A controlled prospective study.', 'Tertiary care centre.', 'Twenty healthy women in active labour and 20 healthy pregnant women not in labour (controls) matched for maternal and gestational age.', 'Venous blood was drawn from women in both groups. Serum levels of lipid peroxidation products and the kinetics of copper-induced oxidation ex vivo were monitored spectroscopically at 37 degrees C by continuous recording of absorbance at 245 nm.', 'Oxidative stress parameters.', 'The initial optical density (OD) at 245 nm, attributed to preformed dienic hydroperoxides and 7-keto-cholesterol (main products of lipid peroxidation), was higher in the labouring group than in the controls (1.30 +/- 0.11 vs 1.18 +/- 0.09, OD 245 nm, respectively, P < 0.001). The lag phase, reflecting resistance of serum lipids to oxidation, was significantly shorter in the labouring group than in the controls (43.2 +/- 1.4 vs 56.2 +/- 4.7 min, respectively, P = 0.01).'] Is active labour associated with increased oxidisibility of serum lipids ex vivo?