Estrogen (or Estradiol)
The major female hormone secreted by the ovaries. A normally menstruating woman ovulates once a month about 14 days after the start of the menstrual cycle. The egg secretes estrogen as it grows. The level of this hormone peaks at the time of ovulation, it then drops and peaks again about a week after ovulation. Estrogen is responsible for the normal growth and differentiation of both the follicle and the egg. It also plays an important role in preparing the endometrial lining where implantation would occur in case of pregnancy. Estrogen also changes the quality and texture of the cervical mucus, making it thinner and more elastic. This allows the normal passage of sperm through the cervix towards the uterus and the tube where it meets the egg. The hormone estrogen is important in helping to maintain healthy vaginal tissue. It also has beneficial effects on bone and the cardiovascular system. For these reasons, estrogen replacement is recommended to most menopausal women. When estrogen is measured on the second or third day of the cycle, its level reflects the health of the eggs. Ideally, a level less than 80 ug/ml is desirable prior to the initiation of ovulation induction or IVF.