Gao J, et al. - This work was designed to determine the influence of the start point of luteal support on clinical pregnancy rate, implantation rate, and live birth rate of in vitro fertilization and embryo transfer (IVF-ET) cycles. Findings suggested that in women undergoing IVF-ET cycles with the use of the GnRH agonist long protocol, the initiation of progesterone supplementation 1 day after oocyte retrieval did not reduce the clinical pregnancy rate, implantation rate, or live birth rate.