The reason why Doctors advise against sleeping on your back or lying on your back for long periods of time is the weight of the uterus and baby puts pressure on the major vein called the vena cava, which can reduce blood flow to the heart then blood flow to the brain and uterus. It can lead to less oxygen for you and your baby then symptoms such as feeling dizzy, short of breath or a bit sick can happen.
Do not feel ultra concerned just take in the following criteria which will help make it all safer.
THINGS TO THINK ABOUT
How Far Along Is Your Pregnancy?
It is from the 3rd trimester that is the trimester you are discouraged from spending too long a time lying on your back.
Are There Medical Concerns?
If you have been told that your placenta has issues or your baby is of low weight then is more important to avoid sleeping on your back as you need maximum blood flow to the baby and your placenta and lying on your back for long periods like when sleeping causes reduced blood flow.
Avoiding the Whole Night Sleeping on Your Back
Try to adopt sleeping positions that are on your side supporting yourself with pillows. Do not panic if wake up lying on your back just simply change positions ideally back into the side lying position. The evidence is not conclusive but there has been some hypotheses that lying on your left side is recommended more than on your right. The reasons being it improves circulation improving nutrients to your baby via the blood to the placenta and also prevents the excess body weight pushing too hard down on your liver. As well as sleeping on your left can help your kidneys get rid of waste products from your body. Use pillows or a pregnancy pillow. If using pillows place one behind your back and one between your knees to help you be comfortable in the side lying position.
Sleeping On Your Tummy
In the early days of the pregnancy there is no risk to sleeping on your stomach but as your stomach becomes bigger you will likely to find it uncomfortable to lie on your stomach
Are You Carrying Multiples
If you are carrying twins or more babies it is likely that the effects of increased weight that happen by the 3rd trimester may begin earlier. Chat to your medical provider regarding their recommendations depending on your individual circumstances.
Exercising On Your Back
It does not mean you can not lie flat on your back at all (unless specifically advised by your doctor) but just try to not do long workouts just on the back ie. do one exercise on your back then change to doing an exercise in another position such as side lying, 4 point kneeling, kneeling and standing. There are symptoms to watch out for such as Nausea, Dizziness, Light Headedness, Racing Heartbeat that need to be avoided and if you experience these symptoms when lying on your back change position or try exercising in different positions. There is a lot more info on this with pics of positions in our Pregnancy Exercise Module.