Does a Blood Pressure Reduction After Dihydralazine, Labetalol Or Pindolol Affect the Human Maternal Placental Circulation?

The maternal placental blood flow was studied in 37 pregnant women in the last trimester of pregnancy. Thirty women had pregnancy induced hypertension defined as a blood pressure of 140/90 mm Hg or more. 0.5 mCi indium-113m was injected intravenously and the radioactivity was registered in a scintillation camera positioned above the placenta. The images obtained were stored in a computer connected on-line to the gamma camera. After computerized summation of the images the placenta could be encircled. The radioactivity in the placental region was plotted as a function of time. From the time-activity curve a uteroplacental blood flow index could be calculated. This index is a semi-quantitative measure of the maternal placental blood flow. After the first blood flow measurement an anti-hypertensive drug was given and a second blood flow measuremnt was performed 30 minues later. When dihydralazine was injected intravenously it was found that the change in uteroplacental blood flow index was correlated to the change in blood pressure. Surprisingly the women that did not respond with a blood pressure reduction diminished their uteroplacental blood flow indices more. No such correlations were seen after labetalol or pindolol treatment.