Maternal-fetal pH difference and fetal scalp pH as predictors of neonatal outcome.

The purpose of this study was to determine if interpretation of fetal scalp pH values would be enhanced by concurrent measurement of maternal venous pH. The last fetal capillary pH obtained before delivery was compared with simultaneous maternal-fetal pH difference as predictors of neonatal outcome assessed by five-minute Apgar scores. Fetal scalp pH and maternal-fetal pH difference were significantly correlated with r = -0.72 (P less than .0001). The acidotic fetuses born to acidotic mothers had low maternal-fetal pH differences, and all were nondepressed at birth. A 33% reduction in false negatives was found using maternal-fetal pH difference instead of scalp pH alone. Errors in interpretation of fetal scalp pH can be reduced by the use of maternal-fetal pH difference.