The most dangerous drug in the world: 'Devil's Breath' chemical from Colombia can block free will, wipe memory and even kill. 1  Scopolamine often blown into faces of victims or added to drinks.
To summarize, it appears the best position is left side, followed by right side. After 16 weeks it's best not to sleep on your back, and you probably won't sleep on your stomach. (One way to avoid sleeping on your back is to sew a tennis ball into the back of your pajamas; this works for people who snore, too).
Too much pregnancy sleep. Believe it or not, pregnant women who sleep 10 or more hours per night had detrimental health effects, including a systolic pressure that is higher in the third trimester, as compared to those who slept 9 hours.