Endometrial preparation for cryotransfer: a gallery of protocols

Kateryna Babenko calls preparation for frozen transfer "the art of cryoprotocols," whose result should be "masterpieces" — a living, healthy mother and child, not merely a positive test.

She opens with an interactive vote: what does the audience choose more often — HRT or a natural cycle. Historically, both worldwide and in Ukraine, the hormone-replacement (HRT) protocol was used more: it is simple, controllable, convenient for timing, created over 30 years ago to synchronise with a donor.

However, HRT is associated with a somewhat lower live-birth rate and a higher risk of early loss than the natural cycle. The key mechanism is the absence of a corpus luteum and the vasoactive factors it produces.

Perinatal risks of the artificial cycle are higher: the risk of pre-eclampsia rises almost twofold in singleton and more in multiple pregnancy. A meta-analysis shows that using a natural cycle can prevent a share of adverse outcomes per 1,000 women.

Target groups for the long protocol are examined (premature ovarian insufficiency, fibroids, adenomyosis): large studies showed no significant advantage of the long agonist protocol over standard HRT or the natural cycle; in adenomyosis, adding aromatase inhibitors may help.

Hence the shift "from efficiency to safety": the aim is not to create a cycle artificially but to use the patient's own reproductive physiology. This brings natural and modified cycles to the fore.

Natural cycles come as "wild" ones (monitoring LH, progesterone, follicle collapse), trigger-modified (hCG fixes the day) and progesterone-modified (exogenous progesterone instead of a trigger).