What happens in a mock cycle?
A mock cycle is a practice frozen embryo transfer cycle without an embryo. The surrogate takes the same medications on the same calendar as a real transfer, and the clinic watches how her body responds. Nothing is transferred, so nothing is at stake except information.
A typical mock cycle runs about 3 to 4 weeks:
- Baseline. An ultrasound and blood work at the start of her period confirm her ovaries are quiet and her lining is thin. Some clinics first suppress her cycle with Lupron.
- Estrogen. She takes estrogen by pill, patch or injection to build the uterine lining.
- Lining check. An ultrasound measures the lining. The clinic looks for about 7 millimeters or more with a trilaminar, or triple-line, pattern, and checks her hormone levels in blood.
- Progesterone. At many clinics she then starts progesterone, often progesterone in oil, for the same number of days as before a real transfer.
- Procedures, if ordered. A mock transfer, an ERA biopsy, or both, on the day a real transfer would happen.
- Stop. She stops the medications, and her period follows.
What the clinic learns: how quickly her lining grows, how thick it gets, which form of estrogen she absorbs well, and whether any dose needs to change. If her lining is slow, the clinic can adjust the real protocol in advance instead of canceling a cycle with your embryo waiting.
What is a mock transfer?
A mock transfer, sometimes called a trial transfer, is a rehearsal of the transfer procedure itself. The physician passes a thin, soft catheter through the cervix into the uterus, usually under ultrasound guidance, without an embryo.
It maps the path. The physician learns the length and angle of the cervical canal and the shape and position of the uterus. If the cervix is tight or curved, the clinic knows before the real day and can plan for it, so the actual transfer is quick and smooth.
A mock transfer takes a few minutes and feels much like a Pap smear. Some clinics do one at the screening visit, others during a mock cycle, and some immediately before the real transfer.
| Mock cycle | Real FET cycle | |
|---|---|---|
| Medications | Estrogen, and progesterone at many clinics; sometimes Lupron first | Estrogen and progesterone; sometimes Lupron first |
| Monitoring visits | Baseline ultrasound and blood work, then one or two lining checks | The same, plus a beta hCG pregnancy test 9 to 11 days after transfer |
| Procedures | Sometimes a mock transfer, an ERA biopsy, or both | Transfer of one thawed embryo |
| Duration | About 3 to 4 weeks, then medications stop | About 4 to 6 weeks to the pregnancy test; medications continue to about 10 weeks if pregnant |
| Compensation | $500 medication start fee when medications begin; any separate mock-cycle fee is set in the agreement | $1,000 transfer fee per transfer, plus the $500 medication start fee |
What is an ERA, and when is it worth doing?
An ERA, or endometrial receptivity analysis, is a test of timing. The idea is that the lining is ready for an embryo during a limited window, and for some women that window opens earlier or later than usual.
In a mock cycle with an ERA, the surrogate takes progesterone for the same number of days she would before a real transfer. On the planned transfer day, the clinic takes a small sample of the lining with a thin catheter, in an office procedure that causes brief cramping. A lab reads the activity of genes in the sample and reports whether the lining was receptive on that day. If it was not, the report suggests shifting the timing of progesterone for the real transfer.
Is it worth doing? The evidence is mixed. Several trials have found no benefit for first transfers. Some clinics use the ERA after repeated failed transfers with good-quality embryos, when timing is one of the few remaining questions. Because a surrogate has already carried a healthy pregnancy, many clinics do not order one for her unless a transfer has failed. Your clinic decides.
When do clinics require a mock cycle for a surrogate?
Not every clinic requires one. Many go straight to the real transfer for an experienced surrogate with a documented good lining from a previous cycle.
Clinics more often ask for a mock cycle:
- For a first-time surrogate whose response to the medications is unknown.
- When her medical history suggests a thin lining, or a uterine procedure has been done since her last pregnancy.
- After a failed transfer, to check the lining and timing before using another embryo.
- When the clinic wants an ERA.
Mock cycles are usually done during medical clearance, after the surrogate's screening and before the real transfer cycle, or after a failed transfer. Your clinic's reproductive endocrinologist makes the call. You can see where this step sits for the surrogate on the surrogate process page.
How long does it add to the timeline?
About a month. The mock cycle itself takes 3 to 4 weeks. After it ends, the surrogate usually waits for her next period before the real cycle can start, and an ERA result takes time to return from the lab.
In the context of the whole journey, PLS plans the medical cycle at 2 to 3 months, and a mock cycle falls inside or just before that window. For many parents the extra month is a fair trade, because a lining problem found in a mock cycle does not cost a cycle with an embryo. The real transfer calendar is laid out on the frozen embryo transfer protocol page.
Is the surrogate compensated for a mock cycle?
A mock cycle asks real work of a surrogate: daily medications, sometimes injections, monitoring visits and possibly a biopsy. PLS surrogates receive the $500 medication start fee when they begin medications. Whether a separate mock-cycle fee applies is set in the surrogacy agreement; confirm the current PLS schedule.
Monitoring and travel costs are paid from the intended parents' independent escrow, not by the surrogate. Lost wages for appointments are reimbursed under the agreement. Side effects of the medications are covered on the medication side effects page.
This page gives general information about mock cycles. It is not medical advice. Your clinic decides whether a mock cycle is needed and sets every dose.
Sources
- ASRM (American Society for Reproductive Medicine), guidance on frozen embryo transfer and on practices using gestational carriers. https://www.asrm.org/
- SART (Society for Assisted Reproductive Technology), patient information on frozen embryo transfer. https://www.sart.org/