We have suggested that the placental clearance of maternal plasma dehydroisoandrosterone sulfate (DS) through estradiol (E2) formation (PC-DSE2) is reflective of uteroplacental blood flow (F). Clewell and Meschia13 suggested that PC-DSE2 is related to F as follows: Cobs = F(1-e- C F), where Cobs = PC-DSE2 and C = total placental clearance of maternal plasma DS. This equation contains two unknown quantities, F and C. To solve the equation, Clewell and Meschia assumed that C was constant. Using 19.7 ml/min for C, they allowed PC-DSE2 to vary widely and computed F. Upon finding that F was unrealistically low for some values of PC-DSE2, they concluded that reductions in PC-DSE2 do not reflect alterations in uteroplacental blood flow. In the analysis of the relationship of F to PC-DSE2, it is important to know the value of C. Since the direct measurement of C is not possible at this time, we have evaluated C by measuring the difference between the metabolic clearance rate of DS (MCR-DS) prior to and immediately following delivery. Any change in MCR-DS before and after delivery should be a reflection of the amount of maternal plasma DS cleared by the placenta through all metabolic routes including PC-DSE2, providing nonplacental clearances of maternal plasma DS before and immediately after delivery are the same. We measured MCR-DS and PC-DSE2 in 15 pregnant women within 5 days before delivery and repeated the MCR-DS measurement in these women beginning 90 minutes after delivery. Among these 15 women, C ranged from a low of 4.7 ml/min in a woman with severe pre-eclampsia to a high of 28.5 ml/min in a woman with twins. In addition to the finding that C varied widely, it was also ascertained that PC-DSE2 was positively correlated with C (r = 0.908; p < 0.001). The finding that low or high values for PC-DSE2, observed in complicated pregnancies, were associated with similar changes in C is suggestive that a change in PC-DSE2 is reflective of a change in uteroplacental blood flow.
ASJC Scopus subject areas
- Obstetrics and Gynecology