Progesterone in Pregnancy: Useful but not a panacea

The hormone progesterone (named for its ability to “promote gestation”) is essential for a healthy pregnancy. Indeed, research over the last several years suggests that low levels of this hormone may be the most common reason for preterm labor. This has been an important finding, allowing doctors to prescribe progesterone to women at risk of a premature delivery (they’ve already had a preterm birth). This week, the New England Journal of Medicine published two articles that can help physicians more accurately target women that can be helped by progesterone.

One study found that when women with a shorter than normal cervix—the funnel shaped transition between the womb and vagina—were given progesterone starting late in the second trimester, it reduced the risk of a preterm delivery by about 50 percent. The other study found, however, that women carrying twins did not appreciably reduce their risk with this same strategy. That’s not surprising since there is probably a different triggering event in these two scenarios. Women with a shortened cervix may have a uterine muscle that isn’t able to stretch rapidly enough to accommodate the growing baby. Progesterone helps relax the muscle fibers so that they can stretch more easily. In a twin pregnancy however, it is more likely that the placenta is unable to meet the nutritional needs as the babies enter the accelerated growth phase of their third trimester. If you’re pregnant with twins, your best strategy is to promote uterine blood flow through good nutrition and regular exercise as well as good prenatal care to monitor the growth of your babies. For many others, progesterone remains an excellent strategy to reduce the incidence of preterm births.