During pregnancy, the placenta makes high levels of the hormone progesterone, which helps support the pregnancy. A drop in progesterone levels is thought to be one of many factors that help start labor contractions.1
Studies have shown that progesterone treatment in the second trimester helps lower the risk of preterm birth. This means that, although some women still delivered prematurely, progesterone treatment helped more high-risk women carry their pregnancies longer than a placebo treatment did.2, 3 (In this case, "high-risk" means that you have had a preterm birth at least once.)
Experts say that bigger studies are needed before they can say that progesterone treatment helps babies. In some studies, newborns tend to weigh more after their high-risk mothers have had progesterone treatment. This may be because a longer pregnancy gives a baby more time to grow.3
There is no evidence that progesterone treatment prevents early miscarriage.
Progesterone is a new treatment, and the type of progesterone used in this research, 17 alpha-hydroxyprogesterone caproate, is not available in all areas of the country.
The American College of Obstetricians and Gynecologists (ACOG) recommends to doctors that weekly progesterone injections only be considered for women who are at high risk for preterm labor. This is based on studies of women who have had a previous spontaneous preterm birth (before 37 weeks).4 Further research is necessary before other high-risk women, such as those who are pregnant with twins or more or women who already have signs of preterm labor, can be considered for progesterone treatment.
References
Citations
Da Fonseca EB, et al. (2003). Prophylactic administration of progesterone by vaginal suppository to reduce the incidence of spontaneous preterm birth in women at increased risk: A randomized placebo-controlled double-blind study. American Journal of Obstetrics and Gynecology, 188(2): 419–424.
Meis PJ, et al. (2003). Prevention of recurrent preterm delivery by 17 alpha-hydroxyprogesterone caproate. New England Journal of Medicine, 348(24): 2379–2385.
Mackenzie R, et al. (2006). Progesterone for the prevention of preterm birth among women at increased risk: A systematic review and meta-analysis of randomized controlled trials. American Journal of Obstetrics and Gynecology, 194: 1234–1242.
American College of Obstetricians and Gynecologists (2003). Use of progesterone to reduce preterm birth. ACOG Committee Opinion No. 291. Obstetrics and Gynecology, 102(5): 1115–1116.
Credits
| Author | Kathe Gallagher, MSW |
| Editor | Kathleen M. Ariss, MS |
| Associate Editor | Pat Truman |
| Primary Medical Reviewer | Joy Melnikow, MD, MPH - Family Medicine |
| Primary Medical Reviewer | Kathleen Romito, MD - Family Medicine |
| Specialist Medical Reviewer | William Gilbert, MD - Perinatology |
| Last Updated | January 19, 2007 |
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