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Estradiol, also called E2, is a type of estrogen that is released by the ovaries in different amounts throughout the menstrual cycle. An overly high amount of this sex hormone can lead to infertility because it can cause problems with the ovarian reserve, which is why some birth control pills use estradiol to help prevent pregnancy. Thus, like other female sex hormones, estradiol and pregnancy are related. Women who are struggling with infertility can have their estradiol levels tested, usually at the same time as the screening for follicle-stimulating hormone (FSH).
E2 is often considered the most important type of estrogen because it plays a major role in ovulation. In the beginning of the menstrual cycle, the level of estradiol is consistent, but it increases sharply in the middle of the cycle. At about the same time, the luteinizing hormone (LH) level increases, prompting ovulation. When ovulation is over, the level of estradiol decreases, only to increase again when the corpus luteum forms. For this reason, estradiol and pregnancy are said to be closely related, because it is not possible to become pregnant without ovulating.
Women who have been trying to become pregnant for a long time might get tests done to determine the reasons for infertility. One of the most common screenings measures the amount of estradiol, which can determine whether the ovarian reserve is sufficient to achieve pregnancy. In many cases, this test is done at the same time as the FSH test, which checks for extremely low or high levels of the follicle-stimulating hormone to determine the reasons for infertility or menstrual irregularities. Both tests usually are performed on the third day of the menstrual cycle, and they often consist of a blood draw. The results typically are available one day after the screening takes place.
In some cases, women who are in the early stages of pregnancy undergo the estradiol test to make sure the placenta and fetus are developing properly. This is because estradiol and pregnancy are believed to be related in that the hormone increases blood flow to the uterus and stimulates the breasts to grow. In addition, estradiol is believed to soften the cervix during the pregnancy, making childbirth possible.
On the other hand, the connection between estradiol and pregnancy is sometimes used to prevent conception. Many hormonal birth control pills contain a derivative of this hormone to prevent ovulation, because high levels of estradiol often hinder the ability to ovulate. The pills that contain this hormone also usually feature progestin, which can further inhibit ovulation. Thus, the relationship between estradiol and pregnancy can be used either to help or to hinder fertility.