Later, steroidogenic factor-1 (SF-1) expression-dependent Bmal1-deleted female mice (Bmal1SF1d/d) were demonstrated to fail embryo implantation, which could be rescued by P4 supplementation or normal ovarian transplantation [35], indicating that poor ovarian production of P4 is one of the main causes for infertility of Bmal1 KO female mice. This evidence concerns the gene BMAL1 and Infertility.