Intrinsic and laboratory determinants of IVF success

Published 23 July 2019

Topics in this third review of embryology sessions from the oral presentation programme in Vienna include the timing of embryo transfer, extended embryo culture, paternal age, embryo arrest, and the effect of trophectoderm morphology grade - from Session 78.

The session opened with a study on the importance of exact transfer timing on live birth rate. This Australian study was a retrospective analysis of euploid blastocysts after PGT-A testing and compared LBR between transfers occurring 120 ±12hrs post-ovulation to transfers outside this window. A multivariate regression analysis showed a positive correlation of LBR with that optimum timeframe and underlined the significance of embryo-endometrial synchrony. A Japanese group also presented data addressing the impact of extended embryo culture. In a retrospective analysis, they found that the LBR after day 7 single frozen embryo transfers was comparable to day 6 when the following factors were taken into consideration: maternal age (<39), time from insemination to blastulation (143h), expansion time (19h) and the blastocyst diameter (210 µm).

Another Australian study addressed concerns of performing assisted hatching in the same dish where the embryo is destined to continue its development. Their centre compared PGT cycles where laser-assisted hatching was performed in the main embryo culture dish or in a second dish. They concluded that moving the embryo to another dish for hatching had no benefit: a retrospective analysis of 6187 embryos revealed that embryonic development was not impaired when the procedure was performed in the same culture dish.

Age was another topic of discussion. First the effect of paternal age on clinical pregnancy in ART was highlighted with data from 4271 subjects at a London IVF centre. Male partners aged above 50 had significantly lower chance of successful ART, with clinical pregnancy rate inversely proportional to male age. The take-home message was that it is not only female age which determines IVF outcome; male partner’s age is additionally important.

Next, a mouse-model study presented by Bjorn Heindryckx, a former co-ordinator of ESHRE's SIG Stem Cells, asked if pronuclear transfer could compensate for advanced maternal age or embryo arrest. The Belgian group showed that pronuclear transfer from aged to young mice did overcome inferior embryonic development by improving blastocyst formation rates. Moreover, in a model of two-cell embryo block (NZB/OlaHsd), transfer of pronuclei from a normally developing embryo could recover embryo arrest. Their work raised the possibility of overcoming particular fertility difficulties by enhancing the oocyte/zygote cytoplasm.

Finally, a second Japanese study addressed the hypothesis that the trophectoderm morphology grade could affect infants’ physiological characteristics and gender ratio. The study showed that, although there was no correlation between the birth weight, height or congenital abnormalities in new-borns with the trophectoderm morphology grade, there was a correlation with the gender ratio. By analysing 1109 singletons, the data suggested that a blastocyst with a higher trophectoderm grade was associated with a gender ration towards male.

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