Effectiveness of progesterone supplementation in women presenting low progesterone levels on the day of frozen embryo transfer: a randomised controlled trial oleh Quang Thanh Le, Thi Minh Chau Le, Khue Tu Duong, Quoc Anh Nguyen, Phuc Thinh Ong, Thi Hong Nhung Nguyen, Thi Cam Thu Thai, Matheus Roque, Carlo Alviggi