Arterial oxygen saturation of the fetus during labour (SPO2) measured with a fetal pulse oximeter was compared to the neonatal condition measured by umbilical vein pH and Apgar score. Changes in oxygen saturation (index of desaturation) during the second stage of labour were also compared to neonatal outcome. Fifty-five patients with abnormal fetal heart rate pattern during labour had a continuous monitoring of fetal oxygen saturation using the Nellcor N-400 pulse oximeter. SPO2 measurement during the last 10 min of labour was significantly correlated to umbilical vein pH and to 1-min Apgar score (P = 0.022 and P = 0.025, respectively). A much higher correlation was found between the index of desaturation and umbilical vein pH at birth and with 1-min Apgar score (P = 0.002 and P < 0.001, respectively). When considering the lower value of umbilical vein pH at birth to be 7.20, and the normal value of SPO2 during labour to be > or = 40% (negative test), we observed a 100% negative predictive value of oximetry. If these results are confirmed in a larger series of patients, analysis of the changes in fetal arterial oxygen saturation during labour (index of desaturation) could be a good indicator of the condition of the newborn. A normal SPO2 value during labour could be reassuring in case of abnormal fetal heart rate.