Is progesterone an effective treatment for preventing miscarriage in unexplained recurrent pregnancy loss?

EVIDENCE-BASED ANSWER Progesterone reduces the odds of miscarriage for women who have experienced 3 or more consecutive pregnancy losses (odds ratio [OR] 0.39) compared with placebo, but does not alter outcomes in women with 1 or 2 prior unexplained miscarriages (SOR: B, meta-analysis of small RCTs). An older report from the Royal College of Obstetricians and Gynaecologists (RCOG) found insufficient evidence to assess the effect of progesterone and did not recommend any empiric treatment of recurrent pregnancy loss (SOR: C, expert opinion).