Does progestogen prevent pregnancy loss in women with recurrent miscarriages?

This study investigated the effect of progestogen (PG) in reducing the miscarriage risk. 

They found that PG may reduce miscarriage risk in women with a history of recurrent miscarriage (RMC).

Early pregnancy loss, or miscarriage, is most common in the first trimester. Women that have more than 3 miscarriages are said to have recurrent miscarriage (RMC). In many cases, the cause of RMC is unclear. In early pregnancy, a hormone called progesterone is important. It stimulates the release of growth factors and fluids to support the fertilized egg. This leads the embryo to implant in the uterus and develop into a fetus. Low progesterone levels may increase the risk of miscarriage. 

Progestogen (PG) is a man-made version of progesterone. It binds to the same receptors and has similar actions. Women with a history of RMC are assumed to have low progesterone levels. Doctors may prescribe PG to reduce the risk of miscarriage. However, the results of previous studies were inconclusive. It is unclear if PG reduces miscarriage risk in women with a history of RMC. 

This study included data from 12 clinical trials. 1,856 women with unexplained infertility participated in these trials. All trials involved administering PG to women with a history of RMC. 

PG given early during pregnancy reduced the risk of miscarriage from 27.5% to 20.1%. However, this finding was not statistically significant. The route of administration (tablet, injection or through the vagina) of PG did not have an effect on miscarriage risk. There may be a slight increase in the live birth rate with PG treatment. PG was not associated with any other pregnancy outcomes.

The authors concluded that PG may reduce miscarriage risk in women with a history of RMC.

The quality of the studies was considered low-moderate. This means that we cannot be certain about the results. More controlled studies are needed.