Birth control pills before a frozen embryo transfer (FET) serve primarily as a scheduling and hormonal control tool. They temporarily quiet your ovaries so your fertility clinic can time the next steps of your cycle precisely, rather than waiting on your body’s unpredictable natural rhythm. It feels counterintuitive when you’re trying to get pregnant, but the pills aren’t working against your goal. They’re creating a clean hormonal baseline so the real preparation can begin on a predictable schedule.
How Birth Control Pills Prepare Your Body
The combination of estrogen and progesterone in oral contraceptives suppresses two key hormones your brain normally sends to your ovaries: FSH and LH. These are the signals that trigger egg development and ovulation. By keeping FSH and LH low through a negative feedback loop, birth control pills essentially put your ovaries on pause. No dominant follicle develops, no ovulation occurs, and no functional cysts form that could complicate the start of your FET cycle.
This suppression also synchronizes any small follicles already developing in your ovaries, bringing them to a similar resting state. Think of it as resetting the playing field. When you stop the pills, your body responds to the next set of hormonal instructions (estrogen patches, pills, or injections to build your uterine lining) in a more controlled and predictable way.
Scheduling Is the Biggest Practical Reason
Fertility clinics manage dozens of patients at once, and FET cycles involve carefully timed ultrasounds, blood draws, and the transfer itself. Without birth control pills, your clinic would need to wait for your natural period to arrive, which can vary by days or even weeks from month to month. That unpredictability creates logistical headaches for both you and the clinic, especially if your transfer needs to be coordinated with a specific embryologist’s schedule, lab availability, or your own work and travel plans.
By prescribing birth control for a set number of days, your clinic controls exactly when your withdrawal bleed (the period-like bleeding after stopping the pills) will happen. From that point, every subsequent step can be mapped out on a calendar. You’ll know your approximate transfer date before you even start your lining preparation, which makes planning the rest of your life around treatment much easier.
How Long You’ll Typically Take Them
Most clinics prescribe birth control pills for somewhere between 12 and 30 days before a FET cycle. After you stop, there’s usually a short washout period of about five days before the next phase of treatment begins. The exact duration depends on your clinic’s protocol and scheduling needs. A 2024 committee opinion from the American Society for Reproductive Medicine (ASRM) found no evidence that the specific timing or length of pretreatment with hormonal contraception influences pregnancy or live birth outcomes, so variations from clinic to clinic don’t appear to matter.
During the washout period, you’ll get a withdrawal bleed, and your clinic will likely bring you in for a baseline ultrasound and blood work to confirm your ovaries are quiet and your lining is thin. Once that looks good, you’ll start the medications that build your uterine lining for the embryo transfer.
Does Birth Control Affect Your Success Rates?
This is the question most patients really want answered, and the data is reassuring but nuanced. The ASRM’s 2024 opinion states that birth control pretreatment taken for 12 to 30 days with a five-day washout does not affect clinical pregnancy or live birth rates. European guidelines similarly describe pretreatment with estrogen and progesterone as “probably acceptable” based on safety and efficacy data, though they note the evidence has been somewhat inconsistent across studies.
One area worth knowing about: a study in women with polycystic ovary syndrome (PCOS) found that live birth rates after FET were 49.4% for women who had their period induced by oral contraceptives, compared to 60.2% for women who had spontaneous periods. That difference was statistically meaningful, suggesting that in PCOS specifically, oral contraceptive pretreatment may slightly lower success compared to cycling naturally. However, this was a single study, and the broader body of evidence across all patient populations does not show a significant impact.
If you have PCOS and are concerned, it’s worth raising this with your reproductive endocrinologist. The study also looked at progestin-only pretreatment, which showed a live birth rate of 50.7%, essentially the same as oral contraceptives.
Not Every FET Requires Birth Control
Birth control pills are most commonly used in medicated (also called artificial or programmed) FET cycles, where your clinic takes full control of your hormones using estrogen and progesterone. But there’s another option: natural cycle FET. In a natural cycle, your doctor monitors your body’s own ovulation with ultrasounds and blood work, then times the transfer around it. No birth control pills are needed.
A large systematic review published in Human Reproduction Update found no difference in pregnancy rates between natural cycle and artificial cycle FET. More notably, natural cycles were associated with a lower risk of adverse obstetric and neonatal outcomes, including complications like preeclampsia and abnormal placental development. The review concluded that natural cycle FET should be the preferred approach for women who have regular, ovulatory cycles.
The tradeoff is flexibility. Natural cycles require more monitoring appointments, and the transfer date can shift based on when you ovulate. If your cycles are irregular or you need tight scheduling control, a medicated cycle with birth control pretreatment often makes more practical sense. Many clinics default to medicated protocols because they’re logistically simpler, but if avoiding birth control pills matters to you, ask whether a natural cycle is an option for your situation.
What to Expect While Taking Them
The side effects of birth control pills during FET prep are the same as taking them at any other time: mild nausea, breast tenderness, headaches, mood changes, and spotting. These tend to be most noticeable in the first week or two, especially if you haven’t taken oral contraceptives recently. The symptoms are temporary and resolve after you stop the pills.
Some patients find it emotionally frustrating to take a contraceptive during fertility treatment. That’s a completely normal reaction. It helps to remember that this phase is purely logistical. The pills aren’t treating infertility or preparing your uterus directly. They’re holding your cycle steady so the medications that do prepare your lining can be started at the right time. Once you stop and move into the estrogen phase of your protocol, you’re in the active part of your FET cycle.