When you're pregnant, a prescription to stay in bed might seem like a welcome break. In reality, however, restrictions on movement during pregnancy can pose health risks. Here's what you need to know.

There is no evidence that bed rest during pregnancy — at home or in the hospital — is effective at treating preterm labor or preventing premature birth.

If you've had an episode of suspected preterm labor or you're at high risk of premature birth, your health care provider might recommend activity restriction. This might mean avoiding lifting items heavier than 20 pounds (about 9 kilograms) and limiting recreational exercise, particularly strength training and heavy lifting. It might also include changing your work schedule, if it involves working more than 40 hours a week, night shifts, prolonged standing and heavy physical work.

If you've had a stopped (arrested) episode of preterm labor and you experience an increase in the frequency or intensity of contractions after sex, your health care provider might recommend avoiding sexual activity.

If your water breaks before labor starts (prelabor rupture of membranes), you have a low-lying placenta, or your placenta partially or totally covers your cervix (placenta previa), your health care provider will discuss avoiding activities such as sex and exercise.

Bed rest during pregnancy can pose health risks, including:

• A blood clot in a deep vein, such as a vein in your leg (venous thromboembolism)
• Decreased bone mass (bone demineralization)
• Musculoskeletal and cardiovascular deconditioning
• Stress due to self-blame, child care issues, and concerns about job loss or finances

If your health care provider recommends bed rest or activity restrictions, ask him or her to discuss the reasons. In the meantime, focus on staying healthy and the day you'll be able to hold your baby in your arms.