The effect of maternal position on venous return for pregnant women during MRI

Abstract

Magnetic resonance imaging (MRI) in pregnancy is commonly undertaken in the left lateral tilt (LLT) position to prevent inferior vena cava (IVC) compression and supine hypotensive events, although this may be suboptimal for image quality. The supine position may also have an adverse effect on fetal well‐being. The spinal venous plexus may provide an alternative pathway for venous return in the presence of IVC compression. This study assesses morphology and blood flow of the IVC and spinal venous plexus for pregnant women in LLT and supine positions to ascertain the effect of maternal position on venous return during MRI. Eighty‐two pregnant women underwent phase contrast MRI (PC‐MRI) of the IVC and spinal venous plexus in the supine position; 25 were also imaged in the LLT position. Differences in life monitoring, IVC, spinal venous plexus and total venous return between the two positions were assessed. A linear regression assessed the relationship between flow in the IVC and the spinal venous plexus in the supine position. Increasing gestational age and the right‐sided position of the uterus on IVC and spinal venous plexus venous return were also evaluated. Hypotension symptoms were similar in supine (10%) and LLT (8%) positioning. Supine positioning decreased IVC height (p < 0.004) and flow (p = 0.045) but flow in the spinal venous plexus increased (p < 0.001) compared with the LLT position. Total venous return showed no difference (p = 0.989) between the two positions. Additional measurements of flow in the aorta also showed no significant difference between the two groups (p = 0.866). Reduced IVC flow in the supine position was associated with increasing gestational age (p = 0.004) and degree of right‐sided uterine position (p = 0.004). Women in the left lateral decubitus position who then rotated supine had greater flow in the IVC (p = 0.008) and spinal venous plexus (p = 0.029) than those who started supine. For the majority of women, the spinal venous plexus acts as a complementary venous return system for pregnant women in the supine position, maintaining vascular homeostasis. Further study is needed to assess the effects on the health of the fetus.

Cardiac and placental imaging (CARP) in pregnancy to assess aetiology of preeclampsia

“…The maternal position is, however, known to influence the cardiac measures such as stroke volume and cardiac output, with a potential 16.4% reduction in cardiac output shown in the supine position compared to the left lateral position [ 30 , 38 ]. These results from a reduced flow in the IVC, shown to correlate with gestational age, degree of the tilt and previous position [ 15 ].…”

“…This choice might, in line with previous studies, result in changes in perfusion and oxygenation which needs to be taken into account when comparing absolute values. To allow this in the future, we also measured the flow in the inferior vena cava (IVC) similar to Hughes et al [ 15 ] using the phase contrast protocol as stated above. This was performed in the “placenta” half of the protocol due to the better coil coverage for the IVC.…”

“…All participants were scanned on a clinical 1.5T Philips Ingenia scanner in maternal supine position [ 15 ] using a combined posterior and torso (dStream) coil. Maternal comfort in the supine position was maximised by elevating the woman's head and legs, as well as splitting the scan in two 30-min sessions with a rest break in-between [ 15 ]. Continuous monitoring of electrocardiography, blood pressure and oxygen saturations with frequent verbal checks were maintained throughout the scan.…”

Imaging of heart disease in women: review and case presentation

“…Positioning during image acquisition is also important. Indeed, in the supine position, the gravid uterus can compress the inferior vena cava which may affect cardiac output; to prevent this, pregnant women should undergo imaging in the left lateral tilt position [ 168 ].…”

ISUOG Practice Guidelines (updated): performance of fetal magnetic resonance imaging

“…Generally, organs can be visualized in detail between 26 and 32 weeks of pregnancy, when pathologies related to abnormal development are more fully evolved, but each pregnancy and each fetus will differ. It may become more difficult for the woman to remain comfortable in the scanner with advancing gestation and consideration of left‐lateral offset is recommended 28 , 29 .…”