How do you counsel pregnant patients on sleeping position?

I counsel my pregnant patients to sleep in any position that they find most comfortable! The risk of vascular compromise really comes later in the pregnancy (late second to third trimester), when I encourage them to sleep on their sides, typically with a body pillow between their legs and/or under their belly for added comfort. The risk of IVC compression occurs when the heavier uterus is placing pressure on it for long periods of time (back sleeping); thus, lateral/side sleeping is best. Though...

There is a risk of IVC compression by the gravid uterus with supine or right lateral decubitus positioning, which may decrease preload and cardiac output. In general, I recommend left lateral decubitus or, at the very least, a left tilt with a pillow when supine.