[Changes in acid-base equilibrium according to the type of delivery].

The changes in fetal acid-base equilibrium in the second stage of labour have been studied in two groups of patients: first, one of 48 women who delivered spontaneously and the second of 79 women who pushed as instructed. In each case blood was taken from the fetus at the beginning of the second stage and another sample was taken from the umbilical artery before the newborn could take his first breath. In the first group the mean value of fetal pH at the start of the second stage was 7.34 +/- 0.007 and in the umbilical artery 7.32 +/- 0.006 (p greater than 0.05; on the other hand in the second group the mean value of the intra-uterine pH was 7.35 +/- 0.06 and in the umbilical artery it had gone down to 7.25 +/- 0.009 ( p Less than 0.0005). The mechanisms by which active pushing as instructed causes a drop in pH in the fetus can be attributed to several possible haemodynamic modifications so that one must question the advantages of pushing under instruction.