National Institute of Health Research funded RCT (n=4153 from 48 UK hospitals) found progesterone therapy in first trimester of pregnancy did not result in a significantly higher rate of live births among women with threatened miscarriage overall compared with placebo (live birth rate 75% vs. 72%, respectively; p = 0.08).
Coomarasamy A, Harb HM, Devall AJ, Cheed V, Roberts ET, Goranitis I, et al. Progesterone to prevent miscarriage in women with early pregnancy bleeding: the PRISM RCT. Health Technol Assess 2020;24(33)
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Maternity & Obstetrics 