VENOUS DRAINAGE OF THE HUMAN UTERUS - RESPIRATORY GAS STUDIES IN NORMAL AND FETAL GROWTH-RETARDED PREGNANCIES

OBJECTIVE: To determine respiratory gas relationships between the uterine veins and umbilical vein in normal and pregnancies complicated by intrauterine growth retardation. STUDY DESIGN: Respiratory gases were measured in both uterine veins and the umbilical vein in eight normal and 13 pregnancies with intrauterine growth retardation. RESULTS: No significant differences were found in the placental versus nonplacental uterine veins. There was a significant correlation for umbilical and uterine venous values of PO2 (p < 0.002) and PCO2 (p < 0.004) in appropriate-for-gestational-age pregnancies, umbilical venous PO2 was always less than uterine venous PO2, and PCO2 always greater than uterine. The transplacental gradient was significantly higher in intrauterine growth retarded than appropriate-for-gestational-age pregnancies for both PO2 and PCO2. There was a lower uterine oxygen extraction in intrauterine growth retarded pregnancies (p < 0.05). CONCLUSION: There is no consistent relationship between placental venous drainage in each uterine vein and placental location. The human placenta simulates a relatively inefficient venous equilibrator and the larger transplacental gradients in intrauterine growth retarded pregnancies may reflect differences in both perfusion pattern and placental structure.