Measurement of fetal transcutaneous oxygen tension--problems and potential.

In a series of 39 fetuses, continuous intrapartum transcutaneous PO2 recordings were made using a commercially available skin electrode, applied to the shaven fetal scalp. The weak correlation between transcutaneous measurements and umbilical blood PO2 at delivery is believed to be due to scalp ischaemia produced by 'head to cervix' pressure during labour. This 'tonsure' effect presents a major obstacle to the use of surface electrodes for intrapartum blood gas monitoring from the fetal scalp in clinical obstetrics. Modification of the current technique may allow it to be used reliably for research.