Why You’re Taking Estrogen While Pregnant (or Trying to Be)
In fertility treatment, it’s common to be prescribed estrogen even during early pregnancy or while preparing for a frozen embryo transfer (FET) cycle. This may feel concerning if the prescription packaging says not to take it if pregnant. But rest assured: the estrogen prescribed by your fertility provider is safe and essential for treatment.
Estrogen’s Role in Embryo Transfer
How Estrogen and Progesterone Work Together
The ovary produces both estrogen and progesterone until the placenta takes over hormone production around 8 to 10 weeks into pregnancy. These hormones are critical for preparing the endometrial lining in the uterus. Estrogen thickens the lining, and progesterone causes it to mature—creating an optimal environment for embryo implantation.
Why It’s Necessary in IVF and FET Cycles
Without these hormones, FET cycles would only be possible during spontaneous menstrual cycles. Likewise, donor-egg IVF would only work with frozen embryos, as timing between the donor and recipient could not be synchronized. There is no evidence that medically prescribed estrogen poses any risk to a developing fetus.
Why the Warning Label Is There
The Legacy of DES (Diethylstilbestrol)
The warning label originates from the historical use of a synthetic estrogen called DES in the 1950s and 1960s. DES was prescribed to prevent miscarriage but was later linked to reproductive tract abnormalities and a rare vaginal cancer (clear cell carcinoma) in the daughters of women who took the drug.
Today’s estrogen is not DES. Modern fertility medications use hormones that are biologically identical to those produced naturally by the ovaries and placenta.
Regulations After DES
In response to the DES tragedy, the U.S. government mandated that all reproductive hormones carry warnings stating they’re contraindicated in pregnancy. This includes natural estrogens and progesterones used in IVF and FET cycles. However, this labeling is not based on risk from current medications but instead on a broad regulatory precaution.
What You Should Do
If your fertility doctor has prescribed estrogen or progesterone as part of your treatment plan, you can feel confident that these medications are safe. They are critical to supporting a healthy embryo transfer and early pregnancy. If you ever have concerns about your medication, your fertility care team is always available to answer your questions.
Schedule a consultation to discuss your treatment plan and medication use with one of our specialists.
