The aim of this study was to determine whether dydrogesterone helps to preserve pregnancy in women with threatened miscarriage.146 women who presented with mild or moderate vaginal bleeding during the first trimester of pregnancy were randomised to receive oral dydrogesterone (10mg b.i.d.) (n=86) or no treatment (n=60). Dydrogesterone was continued until 1 week after the bleeding had stopped. All women received standard supportive care.The incidence of miscarriage was significantly lower in the dydrogesterone group than in the untreated group (17.5% vs. 25%; p<0.05). There were no statistically significant differences between the groups with respect to pregnancy complications or congenital abnormalities.Dydrogesterone appears to have beneficial effects in women with threatened miscarriage.