(693) Aortocaval Compression during Maternal Cardiac Arrest: An MRI Study of Uterus-Great Vessel Dynamics Across Trimesters

During maternal cardiac arrest (MCA), two crucial maneuvers to alleviate aortocaval compression caused by the gravid uterus are left uterine displacement (LUD) and resuscitative cesarean delivery (RCD). This study aims to examine the anatomic relationship between the uterus and aorta, as well as the presence of inferior vena cava (IVC) compression, using magnetic resonance imaging (MRI).

Study Design:

Post-acquisition measurements were obtained from MRI imaging of pregnant women with singleton fetuses between 12+4 – 35+0 weeks for various indications. Measurements were obtained with patients in the supine position at the transverse plane just above the level of the aortic bifurcation, including the distance between the left aortic wall and right uterine wall (LAo-RUt) and presence of inferior vena cava (IVC) compression (Figure).

Results:

Fifty MRIs in pregnant patients were analyzed and stratified by gestational age (Table 1). As expected, the LAo-RUt distance increased with advancing gestational age, with a range of 67.7 – 180.5 mm. MRI evidence of compression of the IVC was present in 36% of pregnant patients between 12+0 – 19+6 weeks, 75% of gravidas between weeks 20+0 – 23+6 weeks, and 90% of gravidas between 32+0 –35+0 weeks. The earliest gestational age IVC compression was noted was 15+5 weeks.

Conclusion:

These findings indicate that most pregnant patients experience IVC compression beyond 20 weeks’ gestation due to the uterus overlying the great vessels. LUD and RCD are most likely to be effective in alleviating aortocaval compression after 20 weeks. However, given that 1/3 of patients less than 20 weeks have evidence of IVC compression, LUD and RCD may also play a role in the resuscitation of patients after 15 weeks, especially those in refractory MCA.