Obstetricians have long known that twin pregnancies are at increased risk of preterm birth, or birth before 37 weeks. One treatment OBs use to help prevent preterm birth in women with other risk factors for preterm birth is progesterone, which can be given via the vagina. Researchers in Sao Paulo, Brazil conducted a randomized, controlled trial published in the July 2015 AJOG journal (the Grey Journal) to test if vaginal progesterone can help prevent preterm birth for twins.
They enrolled 390 women who were pregnant with twins at between 18 and 22 weeks pregnant. Half the women were given a progesterone pill to place in their vagina daily and the other half were given a placebo pill. They all took these pills every day until 35 weeks (median compliance was a very good 96%). After all the babes were born, the researchers compared the number of babies born preterm in each group. They found no difference- whether mothers got a fake pill or progesterone, the babies all had a similar risk of being born at less than 34 weeks gestation. They also had no difference in gestational age at birth (how many weeks the pregnancy went before delivery). On average, women gave birth at about 35 weeks. Both groups had similar rates of needing treatments including steroids for preterm labor symptoms.
Unfortunately, this study offers evidence that vaginal progesterone will not help prevent preterm births for twin pregnancies. Hopefully future research will shed light on new interventions that will help this at-risk population.