In later pregnancy (after 28 weeks), it’s safer to go to sleep on your side than on your back When you’re asleep, you spend most time in the position you go to sleep in. For pregnant women, the blood flow going to the baby may be reduced or interrupted if they spend a long time lying on their back. Research has linked this with an increased risk of stillbirth The causes aren’t clear, but it may be that: the weight of the baby and uterus (womb) puts pressure on the woman’s blood vessels if she lies on her back, which reduces the flow of the blood back to her heart and also to the baby, or the