Progesterone has long been hoped to be a remedy for 1st trimester pregnancy loss. Does progesterone help reduce miscarriage risk? The data is ever evolving. In this session we will review 2 landmark studies that helped answer this question (PROMISE, PRISM). We will also cover a 2020 Cochran systematic review that helped change the 2021 NICE practice guidelines on the subject. Lastly, we will also cover the latest data on this from May 2022 (ACOG ACM).