Analysis of sixty consecutive cases of continuous fetal pH measurement.

60 consecutive fetal CTG-pH-registrations (cardiotocography with continuous pH registration) were analyzed in order to find the causes of the nonsuccessful tracings. Of the 60 tracings, 21 were of good quality, 16 partly successful, and 23 nonsuccessful. The monitoring for each patient had lasted for an average of 154 min with the range of 5--530 min. The quality of the pH recordings were not related to the duration of the pH observation, the maternal age and parity, or to the weight of the infant. If the electrode was applied too early (cervical orifice less than 5 cm) there was a greater risk of a nonsuccessful tracing. The drift of the electrode was less than 0.06 pH-units in 90% of the cases. The rate of nonsuccessful tracings is still too high and the difficulty in sterilization, calibration, and application of the electrode is still rather pronounced. At this moment the pH-electrode should be reserved for scientific use.