Our answer? Relax: It is highly unlikely that either of these sleep positions will acutely harm your baby. We do prefer that you sleep on your left, but don't lose any more sleep if you can't pull that position off for an entire night. Here's a quick anatomy lesson that will help you understand why this sleeping position is recommended.
The vena cava is a large vein that begins around the area of your belly button. It is the vein that is responsible for bringing all the unoxygenated blood from your lower extremities to you heart. This blood is delivered to the right side of your heart, sent through your lungs to get oxygen, circulates back to the left side of your heart and expresses out to your brain and body. Specifically, it is sending blood to the uterus, which is providing all the blood and oxygen to your baby. Once the uterus and the baby reach a certain size, the vena cava can become compressed when you lay flat, delaying the return of the blood to the heart. If this occurs for a long period of time, it can potentially decrease the blood flow to your baby. However, if the compression is significant, it will also decrease the blood flow to your head and brain, resulting in dizziness symptoms.
In our practice, we've discovered that every patient's body is different. In some women, the uterus is never heavy enough to cause dizziness, so they will be comfortable on their backs through much of their pregnancy and probably will not have any decreased blood flow to the baby. However, other women find lying on their backs almost instantly causes them to become sweaty and feel light-headed.
Our rule of thumb is: If you begin to feel dizzy, sweaty, nauseous or short of breath at any time while laying flat, turn on your left side. If you are one of these people, we strongly urge you to try to sleep in this position because your body is alerting you that you are experiencing significant venous compression. You can also lay on your right if your hips get numb on the left.
Dr. Yvonne Bohn, Dr. Allison Hill and Dr. Alane Park are the Mommy Docs. They are doctors, but they're also moms with six kids among them. They've welcomed more than 15,000 babies into the world. The Mommy Docs are featured in the TV series Deliver Me on the Discovery Health Channel. For more information on the Mommy Docs, visit MommyDocs.com.
Do you have any questions about healthy pregnancy? Ask the Mommy Docs in the comments section.
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