This review highlights the complex and highly organized physiological and molecular processes involved in successful pregnancy, focusing on the adverse ripple effects that can arise from defects during the peri-implantation period. These defects, such as aberrations in embryo spacing, decidualization, placentation, and intrauterine embryonic growth, can lead to conditions like preeclampsia, miscarriages, and preterm birth. The review emphasizes the importance of understanding the molecular signaling networks that coordinate successful implantation and decidualization to improve natural and IVF pregnancy outcomes. Key factors discussed include the roles of estrogen, progesterone, and various transcription factors and signaling molecules, such as LIF, Hand2, Klf5, and Msx1, in uterine receptivity and implantation. The review also explores the impact of endocannabinoid signaling and the adverse consequences of defective decidualization, including preterm birth and placental abnormalities. Finally, it discusses future research directions, including the identification of reliable biomarkers for uterine receptivity and the manipulation of the receptive window to improve IVF success rates.This review highlights the complex and highly organized physiological and molecular processes involved in successful pregnancy, focusing on the adverse ripple effects that can arise from defects during the peri-implantation period. These defects, such as aberrations in embryo spacing, decidualization, placentation, and intrauterine embryonic growth, can lead to conditions like preeclampsia, miscarriages, and preterm birth. The review emphasizes the importance of understanding the molecular signaling networks that coordinate successful implantation and decidualization to improve natural and IVF pregnancy outcomes. Key factors discussed include the roles of estrogen, progesterone, and various transcription factors and signaling molecules, such as LIF, Hand2, Klf5, and Msx1, in uterine receptivity and implantation. The review also explores the impact of endocannabinoid signaling and the adverse consequences of defective decidualization, including preterm birth and placental abnormalities. Finally, it discusses future research directions, including the identification of reliable biomarkers for uterine receptivity and the manipulation of the receptive window to improve IVF success rates.