Fertility Treatment: What is Estradiol?

Fertility problems are quite common. In the United States, an estimated 10 percent of reproductive age women experience difficulties getting or remaining pregnant. About a third of all infertility cases are due to the woman, another third due to the man and the final third due to both.

Estrogen is a general term used to describe the female sex hormones. While there are many forms of estrogen, estradiol is the most potent natural one, and it plays a critical role in normal reproduction and sexual functioning. The majority of estradiol is produced in the granulosa cells of the ovaries, with some minor contributions by the adrenal glands and fat. If you are a man, you also have some estradiol, produced by your testes and adrenals. Like other sex hormones, estradiol can freely pass through the cell membrane to interact with cytoplasmic receptors. The complex formed by estradiol and its receptor translocates to the nucleus to regulate the expression of genes and the synthesis of proteins.

Role of Estradiol in Female Fertility

Estradiol is a hormone that is critical in the normal growth and development of the female reproductive organs, and the maturation of the egg in the ovary. It is responsible for initiating the surge in follicle-stimulating hormone (FSH) and luteinizing hormone (LH) that induces the ovary to release an egg. Together with progesterone, estradiol prepares the endometrial lining of the uterus for successful implantation of the fertilized zygote.

Estradiol Tests in Infertility Treatment

Every time you undergo treatment for infertility, you will probably undergo a test that will determine the level of estradiol in your blood. In combination with the FSH test, the estradiol test is used to evaluate your ovarian reserve. It's specifically done to determine the quantity and quality of your eggs.

The test is performed during day 3 of the menstrual cycle. Since the level of estradiol in the blood varies with the stage of the menstrual cycle, your reproductive endocrinologist can analyze estradiol levels at day 3 to determine your ovarian reserve. In general, higher estradiol levels indicate problems with FSH and ovarian reserve that can lead to poor ovulation and lower pregnancy rates. The doctor will explain the results of the test to you.

Estradiol in Assisted Reproductive Technologies (ART)

When conventional infertility treatments do not work, your doctor may suggest ART, such as in vitro fertilization and embryo transfer, to help you conceive. In some types of ART, fertilization occurs outside the uterus, and the formed embryo will then be implanted into the uterus.

For a successful implantation to occur, the endometrial lining of the uterus must be properly primed to receive the embryo. Giving estradiol and progesterone prior to implantation will simulate the priming of the endometrium during the normal menstrual cycle. Estradiol causes the proliferation of endometrial cells and glands, which occurs during the first half of the cycle, while progesterone causes the increased secretion of glands during the second half of the cycle. Priming the endometrium makes it more likely that the embryo will successfully attach.