Fetal oxygen saturation (FSpO2) was monitored with the Nellcor Puritan Bennett N400/FS14 system during 16 labors to establish whether FSpO2 was influenced by maternal bearing down efforts in the second stage of labor. Fetal SpO2 is reported for 16 fetuses where neonatal outcome was normal. One hour of continuous data was recorded: 30 min prior to the onset of maternal bearing down efforts and the first 30 min of pushing. The hour was divided into six epochs of 10-min duration. Differences between mean FSpO2 for the two 30 min of monitoring and for each epoch were sought using repeated measures analysis of variance (ANOVA). The mean FSpO2 for the total 30 min prior to the onset of pushing was 49% (95% confidence intervals 46.5-50.6%), compared to a mean of 46% (95% confidence intervals 43.6-48.7%) during the first 30 min of pushing [F (1, 2.25), p = 0.14]. There was no significant decline in mean FSpO2 for each epoch. Apgar scores at 5 min were all > 7 and umbilical arterial pH values were > or = 7.20 (n = 12). We concluded that mean FSpO2 recorded prior to the onset of maternal bearing down efforts was not significantly different to mean FSpO2 during pushing, with normal neonatal outcome.