Why the corpus luteum still matters when transfer happens in HRT. A walk through 40+ years of LH-progesterone evidence — including L'Correli's 1984 study and pulsatile LH measurement at 10-minute intervals — and the structural split between FET protocols with and without a corpus luteum.
Corpus luteum function depends on LH pulsatility — after every pulse there is a progesterone response 40 minutes later. There are more than 22 published luteal-phase support protocols, which sort into two groups: corpus-luteum-supported (natural cycle, modified natural, NPP) and corpus-luteum-free (HRT). The corpus-luteum-free group is associated with higher rates of preeclampsia, hypertensive disorders, postpartum haemorrhage and preterm birth.
Shift FET to natural or modified natural cycle where feasible, especially in patients with cardiovascular or obstetric risk. When using HRT, recognise the missing corpus luteum contribution and supplement progesterone aggressively with day-of-transfer rescue. Use the NPP protocol for scheduling flexibility while keeping the corpus luteum in the loop.
Natural cycle requires more monitoring and limits weekend scheduling. Some patients cannot be moved to natural cycle (anovulation, severe endometriosis). The HRT vs natural cycle obstetric outcome differences are observational; randomised data are still emerging.
FET protocols fall into two broad groups according to the presence of a corpus luteum. In an HRT (artificial) cycle there is no corpus luteum of one's own — the endometrium is prepared with exogenous estrogen and progesterone, and luteal-phase support is mandatory and fully substitutive.
In a natural and modified natural cycle the woman's own corpus luteum is preserved and provides progesterone support partially or fully. This changes both the need for exogenous drugs and, according to a number of data, obstetric outcomes — above all the risk of hypertensive complications.
A review of more than 22 luteal-support regimens shows that there is no single 'gold standard'; the choice of route (vaginal, intramuscular, subcutaneous progesterone, addition of hCG or LH activity) depends on the type of cycle, the progesterone level on the day of transfer and the individual response.
The practical message of the lecture is to view the role of LH and the corpus luteum as the key to choosing the FET protocol: where there is no corpus luteum, support must be full and controlled; where there is one, it is important not to 'overdose' and to account for the endogenous contribution.
Why does the corpus luteum still matter when we transfer in HRT? A walk through 40+ years of LH-progesterone evidence, three studies (two fundamental, one practical) on luteal-phase support, and where the 22+ existing FET protocols separate into corpus-luteum-supported and corpus-luteum-free strategies.
First Deputy Director General of the «Mother and Child» Medical Center in Kyiv. Candidate of Medical Sciences (PhD), obstetrician-gynecologist and specialist in reproductive medicine.
Author of the lecture "Hormonal Architecture of Frozen Embryo Transfer: Role of LH in HRT and Natural Cycle"
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Audio: UASubtitles: UA32 min
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