Uteroplacental vascular perfusion and blood flow during pregnancy in the guinea pig

The relationships between regional uterine blood flow (UBF), placental blood volume (maternal compartment) and fetal-placental weights and size were determined at specific gestational stages in the guinea pig. Regional variations in UBF were noted between days 27 and 65 of pregnancy (day 0 = ovulation), with the tubal third of the uterus receiving a greater flow rate than the cervical region. The middle portion of the uterus consistently received a lower UBF than did the tubal or cervical zones. Between days 35 and 50 of gestation, UBF rates were consistently lower in the middle portion of the uterus as compared to the tubal and cervical regions in animals possessing exactly three pregnancy sites in a cornu. In contrast, placental blood volume in the maternal compartment from each of the three uterine zones was quantitatively similar, even though lower placental and fetal weights were found in the middle pregnancy sites as compared to either the tubal or cervical zones. When vascular perfusion rates were calculated by determining arterial-venous flow rate differences, both the tubal and cervical uterine zones were found to be preferentially perfused as compared to the middle uterine zone. These studies demonstrate that the correlation between regional UBF rates and fetal-placental development in the guinea pig is primarily due to the greater perfusion rate through the tubal and cervical zones of the pregnant guinea pig uterus, and not due to an expanded vascular volume of the placentae in these zones.