Threatened miscarriage is defined by the National Library of Medicine, Medical Subject Headings (2012 MeSH), as bleeding during the first 20 weeks of pregnancy while the cervix is closed. It is the most common complication in pregnancy, occurring in 20% of all pregnancies. The condition may progress to miscarriage in approximately one-half of cases [1,2], or may resolve. There are problems of definition, as the bleeding may include anything from spots of blood to potentially fatal shock. The treating physician is faced with the question whether any treatment can effectively prevent the pregnancy from being miscarried. Progestational agents have been prescribed since the 1950s in order to prevent miscarriages. There are many theoretical data to support the use of progestagens. Progestagens enhances implantation, affect the cytokine balance, inhibit natural killer cell activity at the feto-maternal interface, inhibit the release of arachidonic acid, prevent myometrial contractility and prevent cervical dilatation. Activation of progesterone receptors on lymphocytes results in the synthesis of a protein known as progesterone-induced blocking factor (PIBF) [3]. PIBF favours the production of asymmetric, pregnancy-protecting antibodies.

Threatened miscarriage is defined by the National Library of Medicine, Medical Subject Headings (2012 MeSH), as bleeding during the first 20 weeks of pregnancy while the cervix is closed. It is the most common complication in pregnancy, occurring in 20% of all pregnancies. The condition may progress to miscarriage in approximately one-half of cases [1,2], or may resolve. There are problems of definition, as the bleeding may include anything from spots of blood to potentially fatal shock. The treating physician is faced with the question whether any treatment can effectively prevent the pregnancy from being miscarried. Progestational agents have been prescribed since the 1950s in order to prevent miscarriages. There are many theoretical data to support the use of progestagens. Progestagens enhances implantation, affect the cytokine balance, inhibit natural killer cell activity at the feto-maternal interface, inhibit the release of arachidonic acid, prevent myometrial contractility and prevent cervical dilatation. Activation of progesterone receptors on lymphocytes results in the synthesis of a protein known as progesterone-induced blocking factor (PIBF) [3]. PIBF favours the production of asymmetric, pregnancy-protecting antibodies.