Estrogen tablets, patches, gels and sprays are not known to be harmful during pregnancy, but if you become pregnant while taking hormone replacement therapy, stop taking it and consult your doctor. Estrogen and progesterone levels are naturally high during pregnancy, so you won't need hormone therapy. Without these hormones, FET cycles would only be possible during spontaneous menstrual cycles. In the same way, in vitro fertilization with donor eggs would only work with frozen embryos, since the time between the donor and the recipient could not be synchronized.
There is no evidence that estrogen prescribed by a doctor poses any risk to the developing fetus. During pregnancy, estrogen has many key effects. It helps develop the placenta1 and the network needed to carry nutrients and waste to and from the growing baby. For the fetus itself, maternal estrogen triggers the development of organs2 such as the lungs, the liver and the endocrine glands.
Combined hormone replacement therapy (estrogen and progestin) may increase the risk of heart attack, stroke, blood clots in the lungs and legs, and breast cancer. Tell your doctor if you smoke and if you have or have ever had a breast lump; breast cancer; a heart attack; a stroke; blood clots or blood clotting problems; high blood pressure; high cholesterol or blood fat levels; lupus (an autoimmune disease in which the immune system attacks healthy parts of the body, such as joints, skin, blood vessels, and organs); or diabetes. If you are having surgery or going to bed rest, talk to your doctor about stopping using estrogen and progestogen at least 4 to 6 weeks before surgery or bed rest. Many trans women are interested in using injectable estrogens.
Estrogen injections tend to cause very high and fluctuating estrogen levels, which can lead to mood changes, weight gain, hot flashes, anxiety, or migraines. In addition, little is known about the long-term effects of these high levels. If injections are used, they should be administered in low doses and taking into account that uncomfortable side effects can occur and that stopping injecting in other ways can cause mood changes or hot flashes. Some trans women have had difficulty getting a consistent supply of injected estrogen because of ongoing problems with the provider.
Realistically, there is no evidence that injections lead to faster feminization or a greater degree of feminization. In my practice, I generally avoid prescribing injections, unless it's under very specific circumstances. Melasma, also called the “mask of pregnancy,” may be related to estrogen, other hormones, or possibly to folate metabolism during pregnancy. Contrary to what many have heard, you can achieve the maximum effect of the transition with estrogen doses that make your blood levels similar to those of a premenopausal cisgender woman.
Since there isn't much research on the use of estrogen for feminization treatment, there may be other unknown risks, especially for those who have used estrogen for many years. High estrogen levels also inhibit follicular stimulating hormone (FSH) and luteinizing hormone (LH), preventing ovulation during pregnancy. Estrogen is also responsible for darkening areoles, nipples, and other areas of the body. Since most non-transgender women go through menopause with a decline in estrogen levels at age 50, this approach is similar to that followed during a woman's natural life and may be especially useful in women with other health risks.
Progestin is added to estrogen in hormone replacement therapy to reduce the risk of uterine cancer in women who still have a uterus. The objective of this study was to investigate whether the use of female sex hormones during pregnancy is a risk factor for mothers and their children to suffer more breast and other estrogen-dependent cancers, as well as for genital malformations in children. Estrogen works together with several different hormones to maintain a pregnancy, and estrogen is vital for a full and healthy pregnancy. The ovary produces estrogen and progesterone until the placenta takes over hormone production at around 8 to 10 weeks of pregnancy.
Low estrogen levels are linked to lower fertility, a higher risk of miscarriage, and a woman with below-normal estrogen may have difficulty getting pregnant. The bottom line is that the main predictor of feminizing effects is probably a lack of testosterone rather than estrogen levels. The main form of estrogen in a woman who ovulates is estradiol, while the placenta produces a form of estrogen called estriol. Progesterone is usually added to a regimen after hormone levels have stabilized after the initial period of onset of administration of estrogen and testosterone.
Hormone replacement therapy works by replacing the hormone estrogen that the body no longer produces.
