Quick answer: ACOG advises avoiding long periods lying flat on your back during pregnancy, and says strengthening the abdominal and back muscles could reduce the risk of back pain.

What ACOG says

ACOG's patient FAQ: "Avoid standing still or lying flat on your back as much as possible. When you lie on your back, your uterus presses on a large vein that returns blood to the heart." On yoga and Pilates: "You should avoid poses that require you to be still or lie on your back for long periods."

Source: ACOG: Exercise During Pregnancy

Committee Opinion 804 explains that lying on your back "after 20 weeks of gestation may result in decreased venous return" and that this "should be considered when prescribing exercise modifications in pregnancy." Its advice to patients is to "avoid long periods of lying flat on their backs". On core strength and back pain it says: "Strengthening abdominal and back muscles could minimize this risk."

Source: ACOG Committee Opinion 804

ACOG does not set a specific time limit. Its concern is the temporary drop in blood pressure that lying flat can cause; the FAQ notes these positions "may cause your blood pressure to decrease for a short time."

Questions about your own pregnancy, birth or recovery belong with your doctor or primary healthcare provider.

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MOMDAY is not a healthcare provider. This article shares general information from public health sources such as ACOG and is educational only, not medical advice, diagnosis or treatment. Always talk with your doctor or primary healthcare provider about what is right for you, and never delay seeking care because of something you read here. If you think you have an emergency, call 911 or your local emergency number.