Obstetric evaluation of fetal acid-base balance

Several techniques may be used to evaluate fetal acid-base status during th e ante- and intrapartum periods. Percutaneous blood sampling (cordocentesis ) may be used to measure standard blood-gas parameters while the fetus is s till in utero, but because of the risks associated with such procedures and the limited clinical utility of the results, this procedure is recommended for blood gas analysis only as part of a research protocol. Intrapartum bl ood specimens may be safely obtained via fetal scalp sampling, but the need for such sampling has been dramatically reduced by the use of other noninv asive tests such as fetal scalp stimulation or vibroacoustic stimulation. F inally, assay of blood obtained from a segment of umbilical cord collected at delivery indicates acid-base status at birth, but the range of normal va lues is wide, and only the most abnormal results have any prognostic signif icance.