Fetal Blood Sampling From Intrahepatic Vein Versus Cord Insertion: Effect on pH and Blood Gases

Abstract

To determine whether venous pH, base excess, and blood gas values collected by antenatal ultrasound-guided sampling from the fetal intrahepatic vein (intra-abdominal umbilical vein, portal sinus, or portal vein) differ from those obtained from the placental cord insertion. Retrospective analysis was done of 1053 clinically indicated fetal blood sampling procedures performed between 1988-1992. One hundred sixty-eight appropriate for gestational age (AGA) singleton fetuses were identified after exclusion of those with conditions believed likely to have impaired fetal blood gas status. Fetal venous pH, carbon dioxide pressure, oxygen pressure, and base excess from 52 samplings at the intrahepatic vein were compared cross-sectionally to those from 116 samplings at the placental cord insertion, using analysis of covariance to correct for gestational age. There was no systematic difference in the blood gas or acid-base values between the two sites of fetal venous blood sampling. Acid-base and blood gas status in AGA fetuses is not affected by the site of sampling. Values obtained at the intrahepatic vein may be interpreted using reference ranges derived from sampling at the placental cord insertion.