Among all hormones, estrogen plays the most important role for your fertility: Estrogen regulates your cycle and ensures that the uterine mucosa builds up in the first half of your cycle. Estrogen also causes your vaginal discharge to become clear and stretchy, making it easier for sperm to travel to the egg. Immediately before ovulation, estrogen reaches its highest level in the cycle, much like the luteinizing hormone (LH).
Fig.: Development of estrogen during the cycle
If you use hormonal contraception, or if the egg is not fertilized after ovulation, your estrogen levels fall, preparing your body for menstruation. If you have sexual intercourse around ovulation and the egg is fertilized, estrogen and progesterone (another hormone) ensure that no further ovulation takes place. The uterine mucosa becomes thicker so that the embryo can nest and continue to grow.
Estrogen is built by the growing eggs in your ovaries and has a big influence on your fertility. Like the number of eggs in the ovaries (the ovarian reserve) decreases over time, estrogen levels also decrease with age, as the following graph illustrates.
Estrogen also influences many other important physical functions. For example, estrogen helps with
- Female genital organ growth during puberty (breast gland, uterus, etc.)
- Bone growth
- Typical female fat distribution (hips, inner thighs, breasts)
- Pubic and armpit hair growth at the beginning of puberty
- Blood flow in the brain
- Nerve cell growth
- The skin’s moisture and nutrient supply
- The heart’s pumping capacity
- Sugar and fat metabolism
Which Estrogens Are There?
The following estrogens can be measured in the blood:
Estradiol is the most effective and, therefore, the most important estrogen in the female body. It is used both directly in the ovaries under the influence of the follicle-stimulating hormone (FSH) and indirectly from adipose tissue in the adrenal gland. When gynecologists speak of “estrogen,” they usually mean estradiol.
Estrone is less effective than estradiol. It is made directly in the ovaries and indirectly from the conversion of certain adrenal cortex hormones (androstenedione and DHEA) in adipose tissue. It becomes more important after the menopause when the aging ovaries produce less estradiol.
Estriol is a degradation product of other estrogens with a low biological effect. However, its concentration increases during pregnancy.
What Do Low Estrogen Levels Mean for Fertility?
Decreased estrogen levels in the blood can be due to
- Ovarian diseases
- Disruption of the estrogen production regulatory mechanisms (secondary ovarian insufficiency):
- Hormonal contraceptives (e.g., the pill, hormonal IUDs, etc.)
- Pituitary gland diseases
- Hypothalamus (part of the intermediate brain) disorders or diseases
What Role Do Estrogen Levels Play in Assisted Reproductive Therapy?
In the context of in vitro fertilization (IVF), hormone injections stimulate immature eggs to grow. Because estrogen is formed by the growing eggs in the ovaries, the estrogen level increases during this time. However, if the estrogen level is too high immediately before the embryo transfer, the chances of pregnancy decrease. In this case, the embryos are frozen and transferred during the following cycle when the estrogen levels have decreased.
Drug Interactions with Estrogen
Estrogens can increase the activity of the neurotransmitter serotonin and enhance the effectiveness of antidepressants from the serotonin-reuptake-inhibitor (SSRI) group. Estradiol should always be checked during hormone therapy.