We find no correlation between duration of the first stage of labor and umbilical artery pH or base excess. We do find a correlation between duration of the second stage of labor and the umbilical artery pH and base excess. However, a prolongation of the second stage with as much as three hours would give an expected lowering of the umbilical artery pH with only 0.05 and of base excess with 2.1 mmol/l for vaginal nulliparas and correspondingly with 0.09 and 3.9 mmol/l in women with previous vaginal births. This effect on pH and base excess is so small that it is hardly clinically relevant and we do not find any support for the belief that a long labor -- in the absence of other risk factors -- is to the disadvantage of the fetus.

We find no correlation between duration of the first stage of labor and umbilical artery pH or base excess. We do find a correlation between duration of the second stage of labor and the umbilical artery pH and base excess. However, a prolongation of the second stage with as much as three hours would give an expected lowering of the umbilical artery pH with only 0.05 and of base excess with 2.1 mmol/l for vaginal nulliparas and correspondingly with 0.09 and 3.9 mmol/l in women with previous vaginal births. This effect on pH and base excess is so small that it is hardly clinically relevant and we do not find any support for the belief that a long labor -- in the absence of other risk factors -- is to the disadvantage of the fetus.