It is generally difficult to force yourself to sleep in any certain position when you are pregnant, but sleeping on the left side (as compared to the back or right side) has been shown to decrease the risk of stillbirths according to a study from New Zealand that was published in 2011. The authors conclude: "This is the first study to report maternal sleep related practices as risk factors for stillbirth, and these findings require urgent confirmation in further studies." The results should be interpreted with caution until more work is done, and a forceful campaign urging pregnant women to sleep on their left side is not yet warranted.
Though the American College of Obstetricians and Gynecologists, the professional organization of all Obstetricians and Gynecologists does not have a firm recommendation for the sleeping position of pregnant women, this study raises concerns about sleeping on your back during pregnancy.
In a chapter on difficulties of sleeping at night, ACOG suggests that women with sleeping problems should consider sleeping on their side …“with a pillow under the abdomen and another between the legs”, but that suggestion applies to women with sleeping problems, not necessarily as a precaution to improve pregnancy outcome.
The advice against sleeping on the back has probably it’s origin from a condition called ‘supine hypotension syndrome’ which is experienced by some women occasionally during pregnancy. The ‘supine hypotension syndrome’ usually occurs in the last trimester of pregnancy, though it can also happen earlier in pregnancy or post-partum. It is characterized by a feeling of dizziness and nausea in a woman lying on her back, occasionally forcing her to change position from the back to the side. In very rare exceptions, more likely on the operating room table and under anesthesia is it possible for the pregnant woman to lose consciousness.
The supine hypotension syndrome is also known as ‘vena cava syndrome’ because it is likely caused by the pressure of the enlarged uterus and the fetus on a large blood vessel, the inferior vena cava, which flows behind the uterus and through the liver towards the heart. This compression of the vein in turn can lead to less blood flowing back to the heart, and eventual decrease in blood pressure (hypotension).
Compression of this big vein can occur when the woman lies directly on her back, but it can also be observed in other positions such as in the pelvic tilt or sitting positions. The low blood pressure usually improves when you move from your back to your side. Because anesthesia may worsen the condition, pregnant women on the operating table are usually placed for precaution slightly tilted on their side with a wedge under their back.
If you do have problems sleeping during pregnancy here some recommendations for a good night’s sleep: