Thickening of endometrium during preovulatory phase is stimulated by

During follicular phase, the primary follicles in the ovary grow to become a fully mature Graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. These changes in the ovary and the uterus are induced by changes in the levels of pituitary and ovarian hormones. FSH stimulates growth of follicles. Growing follicles secrete oestrogen, which is majorly responsible for growth of the endometrium during  pre ovulatory phase i.e., before ovulation.Progesteron helps in growth of endometrium in the post ovulatory phase.