The circadian rhythm is controlled by clock genes, which is crucial for development, reproduction and pregnancy. The precise timing of kisspeptin, gonadotropin-releasing hormone, and gonadotropin secretion in the hypothalamic-pituitary-gonadal axis determines fertility. Additionally, the mouse uterus demonstrated the circadian rhythm regulated by circadian clock genes. The expression level of aryl hydrocarbon receptor nuclear translocator-like protein (Bmal1), a core component of circadian oscillation, was shown to be lower in the endometrium of women who experienced recurrent miscarriages. Bmal1 participates in a variety of physiological processes. It is known that Bmal1-deficient mice were sterile and had damaged gametes and reproductive systems. In addition, hormone secretion is disrupted in Bmal1-deficient mice. Recently, we discovered that uterus-specific Bmal1-deficient mice had impaired placental development and were unable to sustain pregnancy. Additionally, we revealed that time-restricted feeding controlled the uterine clock's circadian rhythm. In humans, we found a higher incidence of hypertensive disorders of pregnancy in pregnant women who had dysmenorrhea in the past at a younger age. These findings suggest that the uterine clock system is a candidate for the new perspective on pregnancy complications.