Natural-cycle IVF — when and how?
Natural-cycle IVF needs no medication. We wait for the single follicle that grows naturally each month and, once it has matured, we retrieve the oocyte. Everything else is the same as in conventional IVF.
What is modified natural-cycle IVF (mNC-IVF)?
In “pure” natural-cycle IVF, the LH hormone can rise too early and the follicle can be lost before we have a chance to perform the retrieval. To avoid this, today we prefer the modified natural cycle: for 2–3 days before retrieval we give a GnRH antagonist (which keeps LH suppressed) together with a small dose of FSH (which helps the follicle finish maturing). This way far fewer cycles are cancelled, with no meaningful added burden on the patient.
Who is it for?
Natural-cycle IVF can be a good choice in four situations. First, in women with low ovarian reserve who did not respond to medication in previous attempts: since FSH injections do not produce more follicles, the natural cycle gives the same result without the cost and burden of stimulation. Second, in women with very high FSH (above 25 IU/L), because their own FSH is already elevated and adding more achieves nothing. Third, in women who do not want stimulation medication for personal, ethical or religious reasons. Fourth, in women who for medical reasons should not undergo stimulation — for example, with a history of hormone-sensitive cancer.
What are the success rates?
Live-birth rates per cycle started are substantially lower than with conventional IVF — around 5–10% for natural-cycle IVF versus 25–35% for conventional IVF in women of comparable age. Cumulatively, after several consecutive natural cycles, the rate may approach that of conventional IVF in good-prognosis patients, at the cost of additional time.
What are the drawbacks?
In natural-cycle IVF only about one in three women reaches embryo transfer. The chain from follicular development to transfer can be broken at multiple points: a premature LH surge and loss of the follicle before retrieval; failure to recover the oocyte; failure of fertilisation; or an embryo of insufficient quality for transfer. These problems also occur in conventional IVF, but the availability of multiple oocytes compensates for the losses there.
Does it make sense to accumulate embryos from multiple natural cycles?
With vitrification, more than 95% of embryos survive thawing. This means we can do several natural cycles, freeze the embryo each time, and transfer them one by one later. This approach is particularly useful when preimplantation genetic testing (PGT-A) is planned, which needs a few blastocyst-stage embryos to be informative.
The alternative strategy — transferring each embryo fresh as it is produced — retains one important clinical advantage: the woman does not have to wait for several embryos to accumulate before attempting pregnancy, and she can re-evaluate the plan after each attempt. The choice between the two strategies is made on the basis of the couple’s individual goals and time constraints, not as a universal rule.
Natural-cycle IVF is neither “better” nor “worse” than conventional IVF — it is a different therapeutic strategy for specific groups of women. The right choice depends on realistic information about success rates, drawbacks, and the available variants (including the modified natural cycle).
Summary.
Natural-cycle IVF is a realistic option for women with low ovarian reserve who do not respond to pharmacological stimulation, for women with very high FSH, and for women who wish to avoid stimulation for personal or medical reasons. The modified natural cycle (with GnRH antagonist and a small dose of FSH) is today the preferred variant, with lower cancellation rates. Live-birth rates per cycle are low, but cumulatively they can approach those of conventional IVF in good-prognosis patients. Thanks to vitrification, we can also collect embryos across several consecutive cycles and use them later.
