Since recent studies has indicated FoxO1’s roles in female reproductive system [22, 27–29] as it is differentially expressed during the proliferative-phase and secretory-phase in human endometrium and mouse estrous cycle [29] as well as a very recent study found that Foxo1 ablated mice were infertile due to defective implantation and invasion [31] we investigated expression and regulation of FoxO1 during mouse peri-implantation period utilizing various experimental pregnancy models. Here, FOXO1 is linked to Infertility.