What is Estradiol?

Estradiol (E2) is the primary estrogen, the major female reproductive hormone, and is produced in your ovaries. As they grow and develop, your egg follicles secrete estradiol, helping to trigger the rest of the reproductive cycle. Estradiol levels vary during the menstrual cycle, and peak at ovulation.

What is the Estradiol Test?

The estradiol test is a simple blood used to measure the levels of estradiol in your bloodstream.

In a normal cycle, the estradiol levels are initially low; and they gradually rise as the follicle matures. With a single follicle, peak E2 levels are about 200-300 pg/ml just prior to ovulation. These high E2 levels causes your cervical mucus to be copious.

Estradiol levels during an IVF cycle

During an IVF cycle, we first downregulate you before starting superovulation. In order to do this, we suppress you with medications containing GnRH agonists, called Lupron or Buserelin. This could be a long protocol (when the Lupron is started on Day 21 of the preceding cycle); or a short protocol (when we start the Lupron on Day 1 of the treatment cycle). We prefer the short protocol in our clinic because it is easier and involves fewer shots! In order to check you are downregulated, we do either a vaginal ultrasound scan on Day 3, to check there are no cysts in your ovaries; or a blood test to check your estradiol levels. Normally, if you are downregulated and your ovaries are quiet, the estradiol level should be less than 50 pg/ml, which means we can proceed with superovulation. However, if the level is more than 50 pg/ml, this means you have not been downregulated. This could be because of poor ovarian reserve; or because you have an ovarian cyst (which can be determined by a vaginal ultrasound scan). If the level is more than 50, we continue the Downregulation for another 4 days and re-check the estradiol level. If it is suppressed or has plateaued, we can proceed with superovulation. If not, we may have to cancel the cycle; put you on birth control pills to suppress the ovaries; and try next month.

Estradiol levels gradually rise as the follicles grow and mature during the IVF cycle and many doctors will measure the estradiol levels frequently during the IVF cycle, to track the growth of the eggs. Remember that the follicle is lined by granulosa cells which produce the hormone estrogen. As the follicle matures, these cells produce increasing quantities of estrogen. Rising levels suggest that the granulosa cells are of good quality, thus indirectly allowing the doctor to conclude that the egg is of good quality. A mature follicle produces about 200 - 300 pg/ml of estrogen. Thus, if you have about 10 follicles on scanning, the doctor can decide to trigger ovulation with HCG when your estradiol level is about 2000- 3000 pg/ml. Remember, however, that the correlation is indirect and is not always accurate. Thus, some women will have good estrogen levels (because their granulosa cells are working fine), but their eggs will be of poor quality This is why estradiol levels should always be interpreted carefully. Two rules apply. Firstly, tracking serial estradiol levels from the same lab to check their trend is very useful. When the eggs are good quality, estradiol levels will double every 1-2 days. Secondly, the levels should be interpreted in conjunction with the ultrasound scan findings.

Estradiol and Ovarian Reserve

Normally, Day 3 estradiol levels should be low because your ovaries are quiet at this time. Elevated levels of Day 3 estradiol tend to indicate a problem with ovarian reserve. When Day 3 estradiol levels are used to assess ovarian reserve, they are measured in conjunction with the Day 3 FSH level.