MRI quantification of human fetal O₂ delivery rate in the second and third trimesters of pregnancy

Purpose The purpose of this study was to estimate fetal O 2 delivery rate in vivo across a range of gestational ages. Toward this, a calibration equation for T 2 ‐based oximetry was derived. Methods Umbilical cord blood of varying hematocrit (Hct) and oxygen saturation (HbO 2 ) levels was prepared and T 2 measured using a T 2 ‐prepared balanced steady‐state free‐precession sequence at 1.5 T. The relationship between blood R 2 = 1/T 2 , HbO 2 and Hct was established based on the model . Experimental R 2 , HbO 2 , and Hct levels were fit to the model‐yielding values of k, and (R 2 of plasma and erythrocytes). Umbilical vein T 2 measured in vivo was then converted to HbO 2 , yielding—together with blood flow rate—the fetal O 2 delivery rate in 22 pregnancies (gestational age 30 ± 3 weeks). Results Constants derived from the fit (R 2 = 0.94) were k = 83.1 s −1 , , and . The and k were found to be larger than those obtained for adult blood, likely the result of differences in dominant hemoglobin type. Data suggest that the use of adult blood calibration could entail errors up 10% in fetal blood HbO 2 . The average umbilical vein blood flow rate (89.5 ± 17.2 mL/min/kg), HbO 2 (84 ± 7%,), and fetal O 2 delivery rate (15.1 ± 3.8 mL O 2 /min/kg) were independent of gestational age. The fetal O 2 delivery rate agreed well with the results obtained with invasive methods at term. Conclusion The present work describes strategies for measuring umbilical vein blood flow rate and HbO 2 in vivo and estimates fetal O 2 delivery rate noninvasively with quantitative MRI during the second and third trimesters of pregnancy. Magn Reson Med 80:1148–1157, 2018.