Background: Supine sleep position during late pregnancy is associated with an increased risk of late stillbirth. When women lie supine during late pregnancy the gravid uterus compresses the inferior vena cava (IVC). This causes dramatic haemodynamic changes, including reduced cardiac output. The maintenance of placental perfusion requires maternal circulatory and autonomic adaptations. Women with supine hypotensive syndrome may be at increased risk of stillbirth due to inability to compensate for the effects of the supine position.
Aim: To examine the haemodynamic responses of women with supine hypotensive syndrome in both the supine and left lateral positions in late pregnancy and compare these responses to those of asymptomatic women.
Methods: We recruited 12 healthy pregnant volunteers without supine hypotension and 10 women with symptoms of supine hypotension. A Skyra 3T (Siemens) scanner was used to obtained axial phase contrast images in supine and left lateral decubitus. Flow was analysed using Syngo.via software (Siemens) to measure net forward volume and maternal heart rate .
Results: Women with supine hypotension had reduced azygos flow, but no other significant difference in flow in other vessels were seen. There were lower flows in the supine position compared to the left lateral in azygos flow, IVC flow (renal and origin), Aortic flow (renal and bifurcation) and lower cardiac output. There was no interaction between supine hypotension and maternal position. No differences were seen in flow in the SVC in relation to group or maternal position.
Conclusion: Flow in the azygos vein in part compensates for the reduced flow seen in the aorta and IVC though this was significantly less in the supine hypotensive group suggesting they do not adapt as well when supine. The lack of difference in superior vena cava flow suggests that the symptoms do not appear to be due to reduced cerebral flow.