when during a menstrual cycle is estrogen lowest
So day one of the menstrual cycle is the first of full bleeding day of the period. A typical cycle is approximately 24 to 35 days (average 28 days for most women). It is not abnormal for a womanÂ¹s cycle to occasionally be shorter or longer. On Day 1 of the menstrual cycle, estrogen and progesterone levels are low. Low levels of estrogen and progesterone signal the pituitary gland to produce Follicle Stimulating Hormone (FSH). FSH begins the process of maturing a follicle (fluid-filled sac in the ovary containing an egg).