In her role as Bree Van de Camp on the hit ABC series Desperate Housewives, actress Marcia Cross has certainly experienced her share of plot twists.

Now in a real life twist of fate, Cross, who is 44 and pregnant for the first time, has been ordered by her doctor to stay in bed for the remainder of her pregnancy. The actress is expecting twins in April. Her publicist Heidi Slan said that the bed rest was just a precautionary measure.

Why would the actress’ doctor take such a measure? It’s probably because Cross’ pregnancy is considered high-risk because of her age and because she is carrying multiple babies.

Dr. Susan Klugman, an obstetrician and gynecologist affiliated with Montefiore Medical Center in New York City, specializes in high-risk pregnancies. She explained that it is not uncommon for doctors to prescribe bed rest for patients who are carrying twins. That’s because with multiple gestations, there is a higher risk of pre-term labor due to the increased stretching of the uterus necessary to accommodate the added volume of two babies.

Another condition that causes the uterus to stretch more is when it is polyhydramious; which means there is extra fluid surrounding the baby.

Advanced maternal age, which is any woman over 35, is another reason doctors prescribe bed rest-- especially if excessive stress, like working in Hollywood, is part of the equation.

Although Dr. Klugman pointed out that in the cases of advanced maternal age, it hasn’t necessarily been proven that bed rest is necessary.

Pregnant women with multiple gestations used to be confined to bed rest in the hospital, but that is seldom done today. The only instances in which hospital confinement would be prescribed are if there is the possibility of very premature birth or the woman’s cervix is very dilated.

By prescribing bed rest, the doctor is attempting to, as Dr. Klugman puts it, “quiet the uterus,” so that the woman is less likely to experience pre-term contractions and pre-term labor. Dr. Klugman noted that bed rest seems to help, but there is no hard scientific proof that it does.

Another instance in which a doctor will prescribe bed rest is before or after a pregnant woman has been given a tocolytic drug. This is a medication that can inhibit labor and slow down or halt the contractions of the uterus. Tocolytic drugs are commonly used to treat premature labor and permit pregnancy to continue, allowing the fetus to grow in size and maturity before being born.

A lot of women who are at risk for pre-term labor are given steroids to mature the baby’s lungs so as to increase the child’s chances of survival. This is done in the hospital with the doctor administering four shots over two days. After the injections have been completed, the woman is sent home and placed on bed rest.

Medication of this type is only administered if there is documented pre-term labor. The documentation in this case would be that the cervix has either softened or dilated.

Dr. Klugman noted that there are disadvantages to prescribing bed rest for pregnant women. As she says, “Women don’t feel great on bed rest. They feel as though they have lost control.”

They can end up becoming depressed or anxious. In terms of adverse physical effects, bed rest puts women at greater risk for blood clots in their legs. For this reason, doctors will require their patients to wear surgical stockings while confined to bed. Women also lose muscle tone. Muscle tone is important for a woman to successfully get through pregnancy and childbirth.

Finally, Dr. Klugman cautioned that a woman who is carrying multiple gestations should carefully consider which hospital she chooses to deliver her babies. The hospital should have a neonatal intensive care unit where they can properly care for a pre-term baby.

So it seems that in Hollywood this time, the body, not the director, had the final word.

Foxnews.com Health contributor Maria Esposito contributed to this report.

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Dr. Manny Alvarez is the managing editor of health news at FOXNews.com, and is a regular medical contributor on the FOX News Channel. He is chairman of the Department of Obstetrics and Gynecology and Reproductive Science at Hackensack University Medical Center in New Jersey. Additionally, Alvarez is Adjunct Professor of Obstetrics and Gynecology at New York University School of Medicine in New York City.

Dr. Manny Alvarez serves as Fox News Channel's senior managing health editor. He also serves as chairman of the department of obstetrics/gynecology and reproductive science at Hackensack University Medical Center in New Jersey. Click here for more information on Dr. Manny's work with Hackensack University Medical Center. Visit AskDrManny.com for more.