A recent study found taking progesterone in the first trimester of pregnancy did not result in a greater rate of live births for women with a history of unexplained recurrent miscarriages (Coomarasamy A et al. N Engl J Med. 2015;373:2141-2148). Approximately 1% of couples experience the loss of 3 or more pregnancies, and for more than half of couples, the cause of recurrent miscarriage is unknown.
The 836 trial participants, who had conceived naturally and were aged 18 to 39 years, were randomly assigned to receive twice-daily vaginal suppositories containing either 400 mg of micronized progesterone or matched placebo from no later than 6 weeks through 12 weeks of gestation.
Slomski A. Progesterone Therapy of No Benefit for Recurrent Miscarriage. JAMA. 2016;315(4):337. doi:10.1001/jama.2015.18977