Estrace is a brand of estradiol, the body’s primary estrogen, and in IVF it is mainly used to thicken the uterine lining so an embryo can implant successfully. Its most common role is in frozen embryo transfer (FET) cycles, where it replaces the estrogen your ovaries would normally produce and gives your clinic precise control over the timing of your transfer.
How Estrace Prepares the Uterine Lining
During a natural menstrual cycle, estrogen produced by your ovaries drives the growth of the uterine lining in the first half of the cycle. It stimulates the cells that make up the lining to multiply and thicken, creating the environment an embryo needs to attach and grow. Estrace delivers that same hormone from an external source.
Estrace also helps the lining transition from its growth phase into a “secretory” state once progesterone is added later in the cycle. This transition is what makes the lining receptive to an embryo. Without adequate estrogen priming first, progesterone alone cannot create a hospitable environment for implantation.
Why It Is Central to Frozen Embryo Transfers
In a fresh IVF cycle, your ovaries are already producing large amounts of estrogen from the stimulation medications, so Estrace is often unnecessary for lining growth. Frozen embryo transfers are different. In a “programmed” or “artificial” FET cycle, the most commonly used FET protocol worldwide, exogenous estrogen like Estrace is given early in the cycle to do two things at once: build the lining and suppress your body from ovulating on its own. This gives your clinic full control over the calendar, letting them schedule the transfer precisely rather than waiting for your body to ovulate naturally.
Natural-cycle FETs are an alternative, but they don’t work for women with irregular cycles and make scheduling unpredictable. The rise in FET cycles overall has been significant in recent years, driven by more clinics doing single embryo transfers, freeze-all strategies to reduce the risk of ovarian hyperstimulation, and the growing use of preimplantation genetic testing. All of these trends mean more patients are taking Estrace than ever before.
Typical Timeline and Protocol
Estrace is usually started in the first few days of your period, often between days 2 and 5 of your cycle. A common dose is 3 mg taken twice daily, though your clinic may adjust this up or down based on how your lining responds. You’ll take it for at least seven days before progesterone is introduced, and often longer.
Before adding progesterone, your clinic will check your lining thickness with an ultrasound. The target is generally 7 mm or greater. Research analyzing over 96,000 embryo transfers found that in FET cycles, live birth rates plateau once the lining reaches 7 to 10 mm. A lining under 6 mm was associated with a dramatic drop in live birth rates in both fresh and frozen transfers. If your lining hasn’t reached the threshold, your clinic may extend the estrogen phase or adjust the dose before moving forward.
Oral vs. Vaginal Estrace
Estrace can be taken by mouth or inserted vaginally, and the route matters more than you might expect. When you swallow an estradiol tablet, it passes through your liver before reaching the rest of your body. This “first pass” metabolism is aggressive: only about 3 to 5% of the ingested dose reaches your circulation intact.
Vaginal administration bypasses the liver entirely. The estradiol is absorbed through the vaginal lining and can act directly on the uterus, resulting in higher bioavailability from the same dose. For this reason, vaginal Estrace is sometimes preferred for patients whose lining has been slow to thicken on oral doses alone. Some clinics use a combination of both routes. Your doctor will choose based on how your lining is responding at monitoring appointments.
How Long You Take It
If your transfer is successful and you become pregnant, you don’t stop Estrace right away. In a programmed FET cycle, your body isn’t producing its own estrogen the way it would in a natural pregnancy, so the medication serves as a bridge until the placenta takes over hormone production. Most clinics have patients stop Estrace around 10 weeks of pregnancy. Progesterone injections typically end around the same time. After that point, the placenta is producing enough hormones on its own to sustain the pregnancy.
Common Side Effects
Because Estrace delivers high levels of estrogen, the side effects are essentially amplified versions of what you might feel before your period. Bloating, breast tenderness, headaches, mood swings, and nausea are all common. These tend to be most noticeable in the first few days and often settle as your body adjusts to a steady dose.
A less common but more serious concern is the increased risk of blood clots. Estrogen raises the risk of venous thromboembolism, particularly deep vein clots in the legs or clots that travel to the lungs. The risk is highest in the first few months of use. For context, the baseline risk of a blood clot in women not taking any hormonal medication is roughly 0.19 to 0.37 per 1,000 women per year. With exogenous estrogen, that risk roughly doubles to triples depending on the dose and formulation. Higher doses carry greater risk. If you notice sudden leg swelling, pain, or shortness of breath while on Estrace, contact your clinic immediately.
Monitoring During Your Cycle
Your clinic will monitor you with a combination of blood draws and ultrasounds while you’re on Estrace. Blood tests measure your serum estradiol levels to confirm the medication is absorbing properly and to watch for signs that your body is trying to ovulate despite the suppression. Ultrasounds track lining thickness and pattern. Clinics look for a “trilaminar” or three-layered lining appearance, which indicates the tissue is responding well to estrogen and is likely to be receptive once progesterone is added.
These monitoring visits typically happen a few times during the estrogen phase, with the most important check occurring around the one-week mark to decide whether it’s safe to start progesterone and schedule the transfer. If anything looks off, your clinic can extend the estrogen phase without compromising your cycle. One of the advantages of a programmed FET is this flexibility: research has shown that starting estrogen stimulation a few days earlier or later in the cycle doesn’t significantly affect outcomes, giving clinics room to adjust.