Prophylactic Administration of Natural Progesterone in the Prevention of Preterm Delivery in Twin Pregnancies: A Randomized, Double-Blind, Placebo-Controlled Trial

In a double-blind, placebo controlled study performed in our Institution, Fonseca et al., investigated the use of micronized natural progesterone, crafted in vaginal capsules of 100mg, for the prevention of preterm delivery. The study involved 142 singleton pregnancies at high risk for premature birth (previous premature birth, cerclage and uterine malformation). The progesterone was introduced from 24 weeks to 34 weeks gestation. The authors observed a significant reduction of premature birth before 37 weeks (28,1% within the placebo group versus 13,8% within the treated group) and below 34 weeks (18,6% within the placebo group versus 2,8% within the treated group). Also, it was observed a reduction in the frequency of the uterine contractions in the progesterone group.

In the only study performed specifically among twin pregnancies, Anna Lisa et al. in 1980, administrated 250mg of 17αOH-PC or placebo (still oil) weekly, in 70 pregnant women with twin pregnancies, beginning before 28 weeks and continuing up to 37 weeks gestation. Seric levels of progesterone, estradiol, estriol, testosterone, and placental lactogenic hormone were also measured weekly. The differences among the achieved results within both groups, according the average in pregnancy duration (36,9 within the treated group, versus 37,3 within the placebo group), the average birthweight and the perimortality rate were not significantly different, as well as the levels of progesterone, estriol, estradiol, testosterone and placental lactogenic hormone. Nevertheless, this study was criticized for starting the use of progesterone at a late stage of pregnancy, in a considerable number of cases.

These studies suggest that in singleton pregnancies with a previous history of preterm birth progesterone treatment may prevent the patients from having subsequent premature births. Nonetheless, the results of these series must not be generalized to all pregnancies at high risk. Additional studies to evaluate the use of progesterone ovules in multiple pregnancies are necessary, as these pregnancies are increasing due to the advanced maternal age at the conception time and also due to the widespread use of assisted reproductive techniques.