The Effects of Maternal Position and Habitus on Maternal Cardiovascular Parameters as Measured by Cardiac Magnetic Resonance.

Objective: To evaluate left ventricular stroke volume (LVSV) and cardiac output (CO) according to maternal position and habitus throughout pregnancy and postpartum using serial cardiac magnetic resonance imaging (c-MRI).

Study Design: This was a prospective study of normotensive nulliparous women using 1.5-T c-MRI performed in both left lateral decubitus and supine positions during three epochs in pregnancy and at 12 weeks' postpartum. Women were stratified according to prepregnancy body mass indices (BMIs) as normal or overweight/obese and compared for LVSV and CO using repeated measures, mixed-random, and fixed-effects model.

Results: Between October 2012 and December 2014, 14 normal-weight (BMI 22.2 ± 1.3) and 9 overweight/obese (BMI 29.1 ± 2.0) women underwent c-MRI. During early pregnancy, position did not alter LVSV or CO for either cohort. Beginning at 26 to 30 weeks and continuing to 32 to 36 weeks, normal-weight women demonstrated significant positional differences for LVSV and CO (both p < 0.01). In contrast, positional differences did not influence these parameters in overweight/obese women. At 12 weeks' postpartum, all influence of position had dissipated for both cohorts.

Conclusion: Maternal position has no effect on LVSV or CO during the first half of pregnancy. In the second half, however, only normal-weight women exhibit significant changes in cardiac parameters when comparing the left lateral decubitus with supine position.