Once your pregnancy has progressed to the 2nd trimester, the uterus has increased significantly in size. Laying on your back will cause it to rest on a blood vessel called the vena cava. The vena cava is the vessel through which all the blood returns from your lower body. If it is obstructed, blood has a harder time getting back to your heart, which means it can’t circulate as quickly, which causes you to feel numbness, tingling, and lightheaded. This also impairs blood flow to your developing baby.
This increase in pressure also causes backaches, may cause difficulty breathing and can place pressure on the digestive system, which can slow transit and cause constipation. The pressure can also be enough to cause hemorrhoids. Try using a body pillow tucked behind your back to help prevent rolling during the night and sleeping with a pillow between your knees to help support your hips.
Some recent studies suggest a correlation between an increase in stillbirths and sleeping on the back.
The best sleep position during pregnancy is “SOS” (sleep on side). Even better is to sleep on your left side. Sleeping on your left side will increase the amount of blood and nutrients that reach the placenta and your baby.
This can cause problems with backaches, breathing, the digestive system, hemorrhoids, low blood pressure and cause a decrease in circulation to your heart and your baby.
Keep your legs and knees bent, and put a pillow between your legs.
These suggestions may not sound completely comfortable, especially if you are used to sleeping on your back or stomach, but try them out. You may find that they work. Keep in mind that you may not stay in one position all night, and rotating positions is fine.
Wedge – Wedge pillows are wedge-shaped cushions that reduce back strain by sliding under your belly to support your growing bump while you're sleeping on your side.
C-shaped – C-shaped pillow that supports and aligns your hips, back, neck and belly. Depending on the direction you place the C-shape in, the entire length of your back or torso can be cushioned and the pillow can be tucked between your knees, too.
U-shaped – The U-shape of this pillow provides bumper cushioning on either side of you. Just rest your head at the bottom of the u-shape and no matter which side you’re sleeping on you’ll have a pillow to squeeze (no more having to bring the pillow with you when you flip sides).
Side-sleeper – It has two puffy, wedge cushions tethered together by a band of stretchy, jersey fabric. One cushion supports your belly while the other supports your back, preventing you from rolling onto your stomach or back in the middle of the night.
Contoured – Similar to the U, but with curves on the long “arms” to give extra support to your lower back and belly.