Normal values for fetal scalp tissue pH during labour.

Normal values for fetal scalp tissue pH during labour were determined by using a glass electrode (Kontron-Roche). A total of 132 recordings was obtained and 84 (64 per cent) were of good quality. After a good quality recording had been obtained, there were 64 infants with an Apgar score of 9 or 10 at one and five minutes after delivery. The 64 recordings showed pH values (Mean +/- 2SEM) of 7.38 +/- 0.12 six hours before delivery and 7.28 +/- 0.12 at the time of delivery. Between the 5th and 55th minutes of the second stage of labour the pH (Mean +/- 2SEM) fell from 7.30 +/- 0.14 to 7.20 +/- 0.13.