Oocyte and zygote development potential in minimal stimulation, natural cycle and conventionally stimulated IVF: an international multi-centre retrospective cohort study.

Purpose
The aim of this research is to assess the development potential of oocytes and zygotes obtained from Natural cycle IVF (NC-IVF), different minimal stimulation IVF (Min stim-IVF) and conventionally stimulated IVF (cIVF) treatment protocols.
Methods
International multi-centre retrospective cohort study including 1483 NC-IVF, 1208 Min stim-IVF, and 1892 cIVF cycles performed in 8 IVF centres between 01.2022 and 03.2023. The five Min stim-IVF protocols analysed included low dose clomiphene citrate, aromatase inhibitors, low dose (≤ 100 IU) gonadotropins, each alone or in combination. For each IVF protocol, we assessed and modelled the transition probabilities of (i) each observed oocyte developing into a zygote, (ii) each observed zygote developing into a gestational sac and (iii) each observed zygote developing into a live birth.
Results
All modelled transition probabilities were found to be maximal in NC-IVF, minimal in cIVF with Min stim-IVF in between. The probability of transition from oocyte to zygote was 0.72 for NC-IVF, 0.56 to 0.65 for Min stim-IVF protocols and 0.54 for cIVF. The probability of transition from zygote to gestational sac was 0.21 for NC-IVF, 0.14 to 0.19 for Min stim-IVF and 0.09 for cIVF protocols and from zygote to live birth 0.16 for NC-IVF, 0.09 to 0.16 for Min stim-IVF and 0.06 for cIVF protocols.
Conclusions
The transition probabilities of oocytes and zygotes appears to be higher in NC-IVF, followed by Min stim-IVF and then cIVF, suggesting that increasing dosages of gonadotropins might have a negative effect on oocyte/zygote development potential.
Trial Registration
Clinicaltrial.gov: NCT05125497. Registration date 03.11.2021.