Women who have given birth to a premature baby are at increased risk of having another early birth. In 2003, two research studies found that treatment with the hormone progesterone reduced the rate of premature birth for some of the women in this group. 

Based on these studies, the American College of Obstetricians and Gynecologists (ACOG) issued guidelines stating that progesterone treatment should be used only by pregnant women who meet three criteria: 

• They have already been pregnant at least once with a single baby (not twins or more).
• With that baby, they began labor on their own and delivered before 37 completed weeks of pregnancy. Medical professionals did not use drugs or other methods to start labor.
• They are currently pregnant again with a single baby.

Since then, other studies have looked at whether progesterone can reduce the risk of premature birth in other high-risk women. One study found that progesterone treatment greatly reduced the rate of premature birth in women who had a short cervix. Most of these women had no prior history of premature birth. A vaginal ultrasound examination can help determine if a woman has a short cervix.

Another study found that progesterone treatment does not reduce the risk of premature birth in women who are pregnant with twins. More than half of twin pregnancies result in premature birth. A number of other studies are currently underway to help clarify which high-risk women may benefit from progesterone treatment.

Studies to date have not reported serious side effects from progesterone for either mother or baby. Progesterone treatment does not appear to increase the risk of birth defects or developmental problems in the baby (through the first 2 years of life). Longer-term follow-up of study participants has not been done.

The studies use two forms of progesterone, an injected form (17P) and a vaginal form (suppositories or creams):

• 17P treatment: Women getting 17P shots to help prevent another premature birth start receiving them between 16 and 20 weeks of pregnancy and continue weekly until 37 weeks. Health care providers must order 17P through special pharmacies that are licensed to mix custom medicines.
• Treatment with vaginal progesterone: Researchers are seeking to determine whether vaginal progesterone treatment works as well as 17P shots in preventing another premature birth. The woman inserts a suppository or cream each night before bedtime.

If you have already had a premature baby or you have a short cervix, ask your health care provider if progesterone treatment might be a good choice for you.

Will Insurance Pay for Treatment?
Not all private insurance companies or state Medicaid programs pay for progesterone treatment. Check with your insurer before starting treatment. Your doctor may also be able to provide information.

This article is based, in part, on guidelines provided by the American College of Obstetricians and Gynecologists (ACOG).

March 2008