Characteristic Circulatory Abnormalities in Pathologic Pregnancies Complex Multiple Pregnancies Monochorionic twins have an increased risk of congenital heart defects, most often pulmonary valve stenosis, but their shared placental circulation forms the substrate for development of TTTS, characterized by activation of the reninangiotensin-aldosterone system and unbalanced intertwined transfusion of these vasoactive substances, as well as volume.111 Early alteration of cardiac function is reflected in discordant diastolic time intervals of the venous duct and in left ventricular strain in affected pregnancies before overt signs of disease are present.161,162 The increased afterload is reflected in the interesting response of the umbilical arteries of the cord to produce hypercoiling (see Fig 6.2).163 In the absence of an obstructed right ventricular outflow tract, noninvasive estimates of the systemic fetal pressures can be estimated from the peak velocity of the jet of tricuspid regurgitation Important tricuspid regurgitation is holosystolic, often with increased duration of the systolic Doppler envelope, with a compensatory shortening of the diastolic filling time It may be associated with abnormal waveforms in the peripheral arterial and venous circulations (e.g., reversal of flow in the venous duct at end-diastole) Twin-reversed arterial perfusion occurs in monochorionic pregnancies where early splitting of the inner cell mass prevents the development of two normally formed twins Ultrasound Doppler examination of these circulations can identify reversed perfusion of the amorphous twin by the normal so-called pump twin Hydrops and cardiac failure may result from volume overload, and the excess cardiac output required to perfuse the abnormal twin may be estimated from the relative volume flows of the umbilical veins of both twins using mathematic modeling.164 Similar circulatory findings of fetal hydrops and cardiac failure may result from volume overload because of a vascular tumor such as sacrococcygeal teratoma and placental chorioangioma Adaptation of this modeling may assist in the monitoring of such pregnancies and guide timing of their treatment or delivery.165 Flow abnormalities associated with vein of Galen aneurysm include reversed flow in the fetal aortic arch due to the steal phenomenon (see Video 6.10) Chest Masses Displacement of the heart and elevation of the venous duct into the chest may occur in diaphragmatic hernia Subsequent alteration of its flow patterns is believed to reduce the flow through the oval foramen into the left side of the fetal heart and may contribute to its reduced growth and coexisting coarctation of the aorta.166 Lung masses such as adenomatous cysts and bronchopulmonary sequestration may displace the heart but usually have minimal effects on fetal physiology Ductal Constriction In the human fetus, ductal flow may be compromised by maternal ingestion of inhibitors of prostaglandins, such as the nonsteroidal antiinflammatory agents and by foods rich in polyphenols Doppler abnormalities in the arterial duct are recognized by increased diastolic and systolic velocities (Fig 6.17) followed by subsequent tricuspid regurgitation due to increased afterload of the fetal right heart FIG 6.17 Doppler profile of ductal constriction is characterized by increased diastolic (D) and often systolic (S) velocities Fistulae of the Coronary Arteries It is relatively easy to demonstrate abnormal vascular connection between the coronary arteries and ventricular cavities, particularly in association with obstructed outflow tracts (Video 6.12) Postnatal coronary arterial steal may be predicted by reversal of flow in the aortic arch, and coronary stenoses or occlusion by the finding of retrograde flow at high velocity (see Fig 6.14) These findings are important to discuss during antenatal counseling because outcomes for these babies may be poor and associated with postnatal death