PG Diploma in Sexology and Psychosexual Counseling. For More Info WhatsApp- 9604715783. At the beginning of menstruation, the concentration of FSH and LH increase, the increase in FSH preceding that of LH by a few days. One of the ovarian follicles becomes highly developed and secretes Estrogen. This developed follicle reaches the size of 1 to 1.5 CMS at the time of ovulation.