Introduction: The fetus and placenta are two highly metabolic entities in the gravid uterus and yet the oxygen consumption (VO2) dynamics between them are unknown in unanesthetized women. In pregnant sheep, an extensively used model of human pregnancy, invasive techniques show that the placenta consumes ~40% of the oxygen available to the gravid uterus near-term(1). The objective was to use MRI to non-invasively measure placental and fetal oxygen delivery (DO2) and VO2 in vivo in late gestation normal human and sheep pregnancies and compare the results between species and to reference data.
Methods: Eleven pregnant women with normal pregnancies were scanned (1.5T Siemens Avanto) at 36+/-1 (mean+/-SEM) weeks (wks; term 40wks) in which DO2 and VO2 were measured in the fetus and placenta. Nine normal catheterized pregnant sheep were scanned (3T Siemens Skyra) at 138+/-1 day (d; term 150d). Blood flow (Q) and oxygen content (C=1.36*Hgb*SO2) were measured in the major blood vessels supplying and draining the placenta (uterine) and fetus (umbilical). Q was measured using phase contrast and C using T1 (Hgb; human only) and T2 (SO2) relaxometry MRI. Measurements were indexed to fetal or placental weight. A t-test was used to compare between species and P<0.05 was considered significant.
Results: DO2 (ml/min/kg fetus) to the gravid uterus (human (H)=53+/-5, sheep (S)=37+/-3, P=0.011) and fetus (H=24+/-1, S=18+/-1, P=0.004) were significantly different between the two species. VO2 by the fetus (H=6.8+/-0.6, S=6.2+/-0.2, P=0.363; ml/min/kg fetus) and placenta (H=2.7+/-0.2, S=3.1+/-0.3, P=0.257; ml/min/100g placenta) were similar between the two species (See Fig 1).
Conclusion: The MRI derived measurements of placental and fetal VO2 in human and sheep were similar to reference sheep data(1,2). Our MRI methods can quantify placental and fetal DO2 and VO2 and has the potential to directly assesses placental function in terms of O2 transport and placental VO2.
2. Rudolph,Wiley Blackwell.2001
Jack R.T. Darby– Postdoctoral Fellow, Early Origins of Adult Health Research Group, School of Pharmacy and Medical Sciences, University of South Australia
Davide Marini– Cardiologist, Division of Cardiology, Hospital for Sick Children and University of Toronto
Mitchell Lock– Postdoctoral Fellow, Early Origins of Adult Health Research Group, School of Pharmacy and Medical Sciences, University of South Australia
Jia Yin Soo– PhD, Early Origins of Adult Health Research Group, School of Pharmacy and Medical Sciences, University of South Australia
Christopher Macgowan– Senior Scientist, Translational Medicine, Hospital for Sick Children and Department of Medical Biophysics, University of Toronto
John Kingdom– Obstetrician, Maternal-Fetal Medicine, Mount Sinai Hospital and Obstetrics and Gynaecology, University of Toronto
Janna Morrison– Head of the Early Origins of Adult Health Research Group, School of Pharmacy and Medical Sciences, University of South Australia
Mike Seed– Division Head, Cardiology, Division of Cardiology, Hospital for Sick Children and Department of Paediatrics, University of Toronto