If you like to sleep on your back, you can sleep in any position in early pregnancy, but as your belly gets bigger, things get more complicated.
From the second trimester on, sleeping on your back can become uncomfortable. The main culprit is your uterus. It's getting heavier and heavier, putting pressure on your bladder and blood vessels, so you may feel suffocated if your circulation is disrupted. Your spine may also cause discomfort for your baby, but don't worry, she'll make sure to point it out to you with her movements!