Oral Presentation 46th Annual Meeting of the Fetal and Neonatal Physiological Society 2019

Maternal Position affects uteroplacental-fetal blood flow and placental oxygenation in late gestation pregnancy: an MRI study (#14)

Peter R Stone 1 , Sophie Couper 1 , Alys Clark 2 , Dimitra Flouri 3 , Rosalind Aughwane 4 , Anna David 4 , Andrew Melbourne 3 , John M D Thompson 1 , Seyed Ali Mirjalili 5
  1. Obstetrics & Gynaecology, University of Auckland, Auckland, New Zealand
  2. Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
  3. School of Biomedical Engineering and Imaging services, Kings College, London, United Kingdom
  4. Institute for Womens Health, University College, London, United Kingdom
  5. Anatomy and Radiological Imaging, University of Auckland, Auckland, New Zealand

Background:

Maternal position in late pregnancy is associated with risk of stillbirth and supine hypotension. Our previous MRI studies quantified the effects of supine position on reduced cardiac output and abdominal aortic blood flow. We aimed using novel MRI techniques, to assess the effects of maternal position on uteroplacental blood flow and measures of oxygenation.

Method:

Eleven healthy pregnant women between 34-38 weeks gestation had MRI scans in left lateral decubitus and supine positions. Axial phase-contrast acquisition was used to scan the internal iliac arteries and umbilical vein. The Syngo viaR (Siemens) algorithm was used to calculate blood flow. A novel technique combining T2 relaxometry and DWI-IVIM (DECIDER) was used to assess oxygenation in the maternal and fetal placental compartments

Results:

Significant reductions in blood flow in both right and left internal iliac arteries were seen when the women were supine compared with left lateral. There was a mean 19.0% (p=0.04) reduction in flow in the right internal iliac artery when supine and a mean 34.1% (p=0.0005) reduction in flow in the left internal iliac artery.

Diffusivity (mm2s-1), a measure related to oxygen transfer in the placenta, was reduced in most subjects when supine with a mean reduction of 4.1%(p=0.07). Fetal oxygen saturation was also reduced by a mean of 7.7%(p=0.12). Flux, the product of these two measures was reduced 11.4% in supine compared to left-lateral (p=0.048).

Conclusion:

In normal late gestation pregnancy, reductions in internal iliac blood flow in the supine compared with the left lateral position are associated with reductions in oxygen diffusivity in the placenta, and small reductions in umbilical venous blood flow and fetal oxygen saturation. Pregnancies complicated by placental mediated conditions such as fetal growth restriction may be additionally adversely affected by the effects of maternal position on placental perfusion and oxygenation.