Chromosome analysis of blastocysts derived from single pronuclear zygotes by array CGH and clinical outcomes by the transfer of single pronuclear zygotes

Embryos derived from single pronucleus are suitable for preimplantation genetic testing

OBJECTIVE

To study and compare the preimplantation genetic testing for monogenic disorders (PGT-M) results, and to evaluate the treatment cycle outcomes of embryos derived from a single pronucleus (1PN) vs. two pronuclei (2PN).

DESIGN

A retrospective cohort study from January 2018 to December 2022 involving in vitro fertilization (IVF)-PGT-M treatment cycles.

SETTING

Single, academically affiliated fertility center.

PATIENTS

A total of 244 patients underwent 351 IVF-PGT-M treatment cycles.

INTERVENTION

Embryo biopsy with molecular testing for a monogenic disorder.

MAIN OUTCOME MEASURES

The molecular diagnosis results and clinical outcomes after the transfer of embryos derived from 1PN and 2PN in IVF-PGT-M treatment cycles.

RESULTS

Embryos derived from 1PN have a significantly low developmental potential with a lower rate of embryos that underwent biopsy compared with 2PN-derived embryos; 1PN-derived embryos demonstrated a significantly lower number of blastocysts (24% vs. 37.9%) and top-quality blastocysts (22.3% vs. 48.1%) compared with 2PN-derived embryos. Lower successfully completed and unaffected PGT-M results were achieved in 1PN compared with 2PN-derived embryos (47.1% vs. 65.5% and 18.7% vs. 31.6%, respectively), with significantly higher abnormal molecular results (39.6% vs. 22.7%). The embryo transfer of 24 1PN-derived embryos with no affected genetic disorder resulted in 5 (20.8%) clinical pregnancies and 4 (16.7%) live births (LBs).

CONCLUSIONS

Within the limits of fewer embryos derived from 1PN that yielded unaffected embryos suitable for transfer, the clinical pregnancy and LB rate of 1PN embryos undergoing PGT-M are reassuring. We, therefore, suggest applying PGT-M to embryos derived from 1PN embryos to improve the cumulative clinical pregnancy and LB rates.

Abnormal cleavage up to Day 3 does not compromise live birth and neonatal outcomes of embryos that have achieved full blastulation: a retrospective cohort study

STUDY QUESTION

Do embryos displaying abnormal cleavage (ABNCL) up to Day 3 have compromised live birth rates and neonatal outcomes if full blastulation has been achieved prior to transfer?

SUMMARY ANSWER

ABNCL is associated with reduced full blastulation rates but does not impact live birth rates and neonatal outcomes once full blastulation has been achieved.

WHAT IS KNOWN ALREADY?

It is widely accepted that ABNCL is associated with reduced implantation rates of embryos when transferred at the cleavage stage. However, evidence is scarce in the literature reporting birth outcomes from blastocysts arising from ABNCL embryos, likely because they are ranked low priority for transfer.

STUDY DESIGN, SIZE, DURATION

This retrospective cohort study included 1562 consecutive autologous in vitro fertilization cycles (maternal age 35.1 ± 4.7 years) performed at Fertility North, Australia between January 2017 and June 2022. Fresh transfers were performed on Day 3 or 5, with remaining embryos cultured up to Day 6 before vitrification. A total of 6019 embryos were subject to blastocyst culture, and a subset of 664 resulting frozen blastocysts was included for live birth and neonatal outcome analyses following single transfers.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ABNCL events were annotated from the first mitotic division up to Day 3, including direct cleavage (DC), reverse cleavage (RC) and <6 intercellular contact points at the 4-cell stage (<6ICCP). For DC and RC in combination, the ratios of affected blastomeres over the total number of all blastomeres up to Day 3 were also recorded. All pregnancies were followed up until birth with gestational age, birthweight, and sex of the baby being recorded.

MAIN RESULTS AND THE ROLE OF CHANCE

Full blastulation rates for embryos showing DC (19.5%), RC (41.7%), <6ICCP (58.8%), and mixed (≥2) ABNCL types (26.4%) were lower than the rates for those without ABNCL (67.2%, P < 0.01 respectively). Subgroup analysis showed declining full blastulation rates with increasing ratios of combined DC/RC affected blastomeres over all blastomeres up to the 8-cell stage (66.2% when 0 affected, 47.0% when 0.25 affected, 27.4% when 0.5 affected, 14.5% when 0.75 affected, and 7.7% when all affected, P < 0.01). However, once full blastulation had been achieved, no difference was detected between DC, RC, <6ICCP, and no ABNCL blastocysts following single frozen transfers in subsequent live birth rates (25.9%, 33.0%, 36.0% versus 30.8%, P > 0.05, respectively), gestational age (38.7 ± 1.6, 38.5 ± 1.2, 38.3 ± 3.5 versus 38.5 ± 1.8 weeks, P > 0.05, respectively) and birthweight (3343.0 ± 649.1, 3378.2 ± 538.4, 3352.6 ± 841.3 versus 3313.9 ± 509.6 g, P > 0.05, respectively). Multiple regression (logistic or linear as appropriate) confirmed no differences in all of the above measures after accounting for potential confounders.

LIMITATIONS, REASONS FOR CAUTION

Our study is limited by its retrospective nature, making it impossible to control every known or unknown confounder. Embryos in our dataset, being surplus after selection for fresh transfer, may not represent the general embryo population.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings highlight the incremental impact of ABNCL, depending on the ratio of affected blastomeres up to Day 3, on subsequent full blastulation. The reassuring live birth and neonatal outcomes of ABNCL blastocysts imply a potential self-correction mechanism among those embryos reaching the blastocyst stage, which provides valuable guidance for clinical practice and patient counseling.

STUDY FUNDING/COMPETTING INTEREST(S)

This research is supported by an Australian Government Research Training Program (RTP) Scholarship. All authors report no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Clinical outcomes of frozen-thawed blastocysts from zygotes with no or one pronucleus for in vitro fertilization and intracytoplasmic sperm injection cycles

PURPOSE

To investigate the clinical outcomes of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) cycles using frozen-thawed blastocyst transfers derived from zygotes with no (0PN) or one pronucleus (1PN).

METHODS

This retrospective study included 7084 0PN, 2238 1PN, and 72,266 two pronuclear (2PN) embryos cultured to the blastocyst stage from 19,631 IVF and 12,377 ICSI cycles between March 2018 and December 2021. Developmental potential and clinical outcomes of 0PN, 1PN, and 2PN embryos were analyzed. A total of 290 0PN-, 92 1PN-, and 1906 2PN-derived single frozen-thawed blastocyst transfers were performed. Chromosome euploid rates of 0PN-, 1PN-, and 2PN-derived blastocysts were analyzed by next-generation sequencing. Euploid 0PN- and 1PN-derived blastocysts underwent subsequent Infinium Asian Screening Array gene chip analysis to detect ploidy alterations.

RESULTS

Available blastocyst rates of 0PN and 1PN embryos were significantly lower than those of 2PN embryos in both IVF and ICSI cycles. Single 0PN and 1PN blastocysts transferred in frozen-thawed cycles resulted in a similar clinical pregnancy rate, miscarriage rate, live birth rate, and neonatal outcome to 2PN blastocysts in IVF and ICSI cycles. Genetic analysis showed that euploid rates of 0PN- and 1PN-derived blastocysts used for ICSI cycles were similar to that of 2PN-derived blastocysts.

CONCLUSION

Our study indicated that 0PN- and 1PN-derived blastocysts resulted in similar clinical outcomes to 2PN-derived blastocysts. The 0PN- and 1PN-derived blastocysts from ICSI cycles can be transferred as well as those from IVF cycles when the number of 2PN-derived blastocysts is insufficient.

The aneuploidy testing of blastocysts developing from 0PN and 1PN zygotes in conventional IVF through TE-biopsy PGT-A and minimally invasive PGT-A

Zygotes without a pronuclear (0PN) or with one pronuclear (1PN) were defined as abnormal fertilization in conventional in vitro fertilization (IVF). The removal of 0PN and 1PN zygotes from conventional IVF cycles has always been controversial. This study aimed to investigate the chromosomal aneuploidy rates of 0PN- and 1PN-derived blastocysts in conventional IVF cycles and to assess the concordance rate between TE-biopsy PGT-A and miPGT-A. TE biopsies and culture media with blastocoel fluid (CM-BF) samples were whole-genome amplified by multiple annealing and looping-based amplification cycle-based single-cell ChromInst method. Next generation sequencing was performed for comprehensive chromosomal screening on a NextSeq550 sequencer using the NextSeq 500/550 High Output kit v2. The aneuploidy rates of 0PN-derived blastocysts were 19.7% for TE-biopsy PGT-A, and 36.1% for miPGT-A; the concordance rate for ploidy was 77.0%; and the sensitivity and specificity were 83.3% and 75.5%, respectively. The aneuploidy rates of 1PN-derived blastocysts were 37.5% and 37.5% by TE-biopsy PGT-A and miPGT-A, respectively; the concordance rate between TE biopsies and CM-BF samples was 83.3%; and the sensitivity and specificity were 77.8% and 86.7%, respectively. Regarding TE-biopsy PGT-A, there were no significant differences in aneuploidy rates among 0PN-, 1PN- and 2PN-derived blastocysts (PGT-M cycles) (19.7% vs. 37.5% vs. 24.3%, P = 0.226), but the aneuploidy rate of 1PN-derived blastocysts was slightly higher than the other two groups. An increase in aneuploidy rates was observed for 0PN/1PN-derived day 6 blastocysts compared to 0PN/1PN-derived day 5 blastocysts (TE-biopsy PGT-A: 35.7% vs. 19.3%, P = 0.099; miPGT-A: 39.3% vs. 35.1%, P = 0.705). The present study is the first that contributes to understanding the chromosomal aneuploidies in 0PN- and 1PN-derived blastocysts in conventional IVF cycles using TE-biopsy PGT-A and miPGT-A. The clinical application value of 0PN- and 1PN-derived blastocysts in conventional IVF should be assessed using TE-biopsy PGT-A or miPGT-A due to the existence of chromosomal aneuploidies.. In terms of consistency, the miPGT-A using blastocoel fluid enriched culture medium is promising as an alternative to TE-biopsy PGT-A for aneuploidy testing of 0PN- or 1PN-derived blastocysts in conventional IVF.

Morphokinetic analysis of pronuclei using time-lapse cinematography in bovine zygotes

The morphokinetics of pronuclei (PN) are considered crucial factors affecting embryogenesis in mammals. Whereas, since bovine zygotes contain a large number of cytosolic lipid droplets, detailed observation of PN has not been performed. In this study, we visualized PN using time-lapse cinematography (TLC) with light microscopy for the first time in delipidated bovine zygotes. The proportions of 0 PN, 1PN, 2PN, and multi-PN in delipidated bovine zygotes were 10.1%, 6.5%, 72.7%, and 10.8%, respectively. Abnormal fertilization, including 1 PN and multi-PN, was observed in 15.6% of blastocysts. The times from IVF to PN appearance, PN fading, and first cleavage in 2 PN bovine zygotes that developed into blastocysts were 10.4, 25.5, and 27.6 h, respectively, which were similar to PN morphokinetics in humans. The 2 PN zygotes showed that the prolonged time from IVF to the appearance of PN and from the fading of PN to the first cleavage negatively affected blastocyst formation. The time from appearance to fading of PN in multi-PN zygotes that developed into blastocysts was longer than that in multi-PN zygotes that did not develop into blastocysts. Besides, among zygotes that developed into blastocysts, the time from appearance to fading of PN in multi-PN zygotes was longer than that in 2 PN and 1 PN zygotes. These results suggest that PN morphokinetic abnormalities are associated with subsequent embryonic development. Observation of PN in bovine zygotes by using non-invasive visible light TLC by delipidation could be a powerful tool to clarify the relationship between PN morphokinetics and developmental competence.