 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. 