Objective: To investigate the relation between umbilical vein blood gas components and the vascular resistance in four fetal arteries in Rh-immunised pregnancies.
Design: A prospective observational study over a 4-month period.
Setting: King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia.
Subjects: Fifteen Rh-isoimmunised pregnant women.
Interventions: Pulsed Doppler examinations of the umbilical artery, fetal internal carotid artery, thoracic aorta and abdominal aorta before transabdominal fetal blood sampling from the umbilical vein on 38 occasions.
Main outcome measures: Doppler flow velocity pulsatility index (PI), systolic/diastolic ratio (A/B) and resistance index (RI) in the four fetal arteries investigated were related to the umbilical vein blood gases and acid-base status (PO2, PCO2, O2-content, CO2-content, HCO3, base excess and lactate concentration).
Results: There were no correlations between the Doppler indices in any of the vessels studied and the blood gases components in the umbilical vein. The ratios between the corresponding Doppler indices in the different vessels were also independent of the blood gases and acid-base status and there were no significant differences in the Doppler indices in the same vessel between fetuses with blood gas values over the 75th centile and those with values below the 25th centile.
Conclusion: This study does not support a reduction in peripheral vascular resistance in the fetal cerebrum in relation to fetal hypoxia in Rh-immunized pregnancies.