The role of dydrogesterone in recurrent (habitual) abortion.

The published evidence regarding the administration of dydrogesterone in the treatment of habitual abortion is summarised in this review. Habitual abortion is defined as the loss of three or more consecutive pregnancies without known maternal or foetal pathology. The immunology of early pregnancy seems to determine the rejection or non-rejection of the allogenic embryo. When peripheral mononuclear cells from recurrent aborters are incubated with progesterone or dydrogesterone in vitro, T-helper (Th)2 cytokines such as interleukin (IL)-4 and IL-6 markedly increase whereas the Th1 cytokine interferon-gamma decreases. Additionally, both progesterone and dydrogesterone are thought to inhibit the activity of natural killer cells at the foeto-maternal interface in humans. Progesterone-induced blocking factor (PIBF) mediates the immunological effects of progesterone and dydrogesterone in pregnancy. It affects various phases of the maternal immune response involving both the cellular and humoral immune system, exerts anti-abortive effects and inhibits the release of arachidonic acid. It also favours the production of so-called asymmetric, pregnancy-protecting antibodies. In rodents, blockade of this factor results in the termination of pregnancy and in women considerably lower levels are found in those with threatened abortion or pre-term labour. In order to draw final conclusions as to the usefulness of dydrogesterone in women with a history of recurrent miscarriage, further controlled, blinded, randomised clinical trials are needed.