KEY POINTS: The ductus venosus (DV) is a dynamic fetal shunt that allows substrate rich blood from the umbilical vein to bypass the hepatic circulation. In vitro studies suggest a direct role of prostaglandin I2 (PGI2 ) in the regulation of DV tone: however, the extent of this regulation has not been determined in utero. 4D flow and T2 oximetry MRI can be combined to determine blood flow and oxygen delivery within the fetal circulation. PGI2 increases DV shunting of substrate rich blood but this does not increase cerebral oxygen delivery.
ABSTRACT: During fetal development, the maintenance of adequate oxygen and nutrient supply to vital organs is regulated through specialised fetal shunts. One of these shunts, the ductus venosus (DV), allows oxygen rich blood to preferentially stream from the placenta toward the heart and brain. Herein, we combine MRI techniques that measure blood flow (4D flow) and oxygen saturation (T2 oximetry) in the fetal circuit to determine whether umbilical vein infusion of Prostaglandin I2 (PGI2 , regulator of DV tone ex utero) directly dilates the DV and thus increases the preferential streaming of oxygen rich blood toward the brain. At 114-115d gestational age (GA; term = 150d), fetal sheep (n = 6) underwent surgery to implant vascular catheters in the fetal femoral artery, femoral vein, amniotic cavity and umbilical vein. Fetal MRI scans were performed at 119-124d GA. 4D flow and T2 oximetry were performed to measure blood flow and oxygen saturation across the fetal circulation in both a basal state and whilst the fetus was receiving a continuous infusion of PGI2 . The proportion of oxygenated blood that passed through the DV from the umbilical vein was increased by PGI2 . Cerebral oxygen delivery was unchanged in the PGI2 s tate. This may be a result of decreased flow from the right to left side of the heart as blood flow through the foramen ovale was decreased by PGI2. We have shown that although PGI2 acts on the DV to increase the proportion of oxygen rich blood that bypasses the liver, this does not increase cerebral oxygen delivery in the fetal sheep. This article is protected by copyright. All rights reserved.