IVF with vitrified donor oocytes is less efficient than using fresh oocytes, but its efficacy remains comparable to that of fresh cycles.
WHAT IS KNOWN ALREADY?
Oocyte vitrification is used to preserve the reproductive potential of oocytes. A small number of randomized controlled trials carried out by experienced groups have shown that this technique provides fertilization, pregnancy, implantation and ongoing pregnancy rates comparable to those of fresh oocytes. However, large registry-based analyses have consistently reported lower live birth rates (LBRs) in cycles using vitrified oocytes. It is not clear whether this decrease may be due to the effect of vitrification per se on the oocytes or to the lower efficiency of the technique, as some of the oocytes do not survive after warming.
Retrospective cohort analysis of 1844 cycles of oocyte donation (37 520 oocytes), each donor in the study provided enough oocytes for at least one reception cycle with fresh oocytes (2561 cycles) and one reception cycle with vitrified oocytes (2471 cycles) from the same ovarian stimulation (sibling oocytes). Overall, 35 654 oocytes were considered in the analysis.
PARTICIPANTS / METHODS
Differences in reproductive outcomes after the first embryo transfer were evaluated using Pearson’s Chi-squared test and regression analysis adjusted for recipient’s age, BMI, sperm origin and state, day of embryo transfer, morphological score and number of transferred embryos. We performed two additional sub-analyses, to test whether the efficiency and/or effectiveness of vitrification/warming impacts reproductive results. One analysis included paired cycles where the same number of fresh and vitrified oocytes were available for ICSI (SAME sub-analysis), while the second analysis included those cycles with a 100% survival rate post-warming (SAME100 sub-analysis).
Fertilization rates and embryo morphological scores were significantly lower (P < 0.001) when using vitrified oocytes moreover, vitrified oocytes also resulted in lower reproductive outcomes than sibling fresh oocytes using both unadjusted and adjusted analyses:
- ongoing pregnancy: 32.1% versus 37.5% P < 0.001 OR 0.88, 95% CI 0.77, 1.00
- live birth: 32.1% versus 31.9%, P = 0.92 OR 1.16, 95% CI 0.90, 1.49
However, when the efficiency of warming was taken into account, reproductive outcomes in recipients became comparable:
- ongoing pregnancy: 33.5% versus 34.1% P = 0.82 OR 1.11, 95% CI 0.87, 1.43
- live birth: 32.1% versus 32% P = 0.97 OR 1.15, 95% CI 0.89, 1.48
Moreover, the conclusion of results of the SAME100 sub-analysis shows that reproductive outcomes were also comparable between fresh and vitrified oocytes:
- ongoing pregnancy: 34.8% versus 32.4% P = 0.42 OR 1.32, 95% CI 0.98, 1.77
- live birth: 32.9% versus 31.0%; P = 0.52 OR 1.27, 95% CI 0.95, 1.71
Indicating that reproductive outcomes of these cycles are affected by the efficiency of the vitrification/warming technique performed rather than the oocyte damage due to the fast cooling process to which oocytes are subjected.