Preimplantation genetic diagnosis by fluorescence in situ hybridization of reciprocal and Robertsonian translocations

Blastocyst conversion rate and ploidy in patients with structural rearrangements

OBJECTIVE

The primary objective of this study was to test the hypotheses that compared to IVF cycles undergoing preimplantation genetic testing for aneuploidy (PGT-A) with or without testing for monogenic disorders (PGT-M), IVF cycles undergoing PGT for structural rearrangements (PGT-SR) will have (1) a poorer blastocyst conversion rate and (2) fewer usable blastocysts available for transfer. Secondarily, the study aimed to compare pregnancy outcomes among PGT groups.

PATIENTS

Retrospective cohort study including cycles started from January 1, 2012, to March 30, 2020, with the intent of pursuing PGT-A, PGT-A with PGT-M, and PGT-SR, with trophectoderm biopsy on days 5 or 6.

RESULTS

A total of 658 women underwent 902 cycles, including 607 PGT-A, 216 PGT-A&M, and 79 PGT-SR cycles. When compared with the blastocyst conversion rate for the PGT-A group (59.4%), and after adjustment for patient age, total number of mature oocytes, BMI, and ICSI, there were no significant differences for either the PGT-A&M (69.7%, aRR 1.03, 95% CI 0.96-1.10) or PGT-SR (63.2%, aRR1.04, 95% CI 0.96-1.13) groups. Compared to the PGT-A group, the proportion of usable blastocysts was statistically significantly lower in the PGT-SR group: 35.1% versus 24.4% (aRR 0.57, 95% CI 0.46-0.71) and the PGT-A&M group: 35.1% versus 31.5% (aRR 0.68, 95% CI 0.58-0.81). Implantation, pregnancy, and miscarriage rates were equivalent for all groups.

CONCLUSION

Patients with structural rearrangements have similar blastocyst development but significantly fewer usable blastocysts available for transfer compared to PGT-A testers. Nevertheless, with the transfer of a usable embryo, PGT-SR testers perform as well as those testing for PGT-A.

Application of improved single blastomere fixation technique in preimplantation genetic diagnosis

To modify a fixation method improving the intensity and clarity of the single blastomeric signal detection by fluorescence in situ hybridization (FISH) in preimplantation genetic diagnosis. 333 cycles of assisted reproduction with preimplantation genetic diagnosis FISH (PGD-FISH) performed in our hospital were analyzed and a total of 3452 single blastomeres were obtained. For the conventional fixation method, the blastomeres were kept in 0.1% sodium citrate with 0.2 mg/ml bovine serum albumin (BSA) for 2-5 min. FISH was performed and the internal relationship between embryo quality and fixed rate, signal detection rate, and signal determination rate was explored. With the modified method, 91.54% of blastomeres were fixed, while 88.30% were fixed with the conventional method. The signal detection rate was significantly increased for the modified group than for the conventional group (compared 98.53% with 94.78%, P < 0.001). Especially, the signal determination rate also showed a significant difference between the two methods (compared 90.51% with 74.17%, P < 0.001). After the development of the fixation method, the fixation efficiency and the signal determination rate were greatly improved, providing more definite diagnosis for the patient. It will hopefully allow more assisted reproduction programs to offer their patients preimplantation genetic diagnosis with FISH.

The application of PGT-A for carriers of balanced structural chromosomal rearrangements

The aim of this study was to analyze differences in chromosomal aberrations and euploidy in embryos of each translocation type and gender of carrier in the case series of 10 couples with balanced translocations who underwent IVF with embryos trophectoderm (TE) biopsy and PGT-A to detect chromosomal aberrations. This is a Case Series (Retrospective study). In each case, controlled ovarian hyperstimulation, oocyte insemination with intracytoplasmic sperm injection (ICSI) and cultivation gave multiple blastocysts, that underwent trophectoderm (TE) biopsy with PGT-A analysis using aCGH and NGS. Number of total unbalanced translocations compared to the number of sporadic aneuploid embryos was 39.6% to 39.6% (50% to 50% of all 37 aneuploid embryos). The highest euploidy rate was in male carrier group - 26.7% and the lowest in the Robertsonian translocation carrier group - 18.2%. Sporadic aneuploidy - 68.2% was highest in Robertsonian translocation carrier group and lowest in female group - 11.1%. Chromosomal aberrations related to translocation were highest in female carrier group - 77.8% and lowest in Robertsonian translocation carrier group - 13.6%. Our study showed that expectancy of total embryo aneuploidy rates will be higher in carriers, than in people with normal karyotype. The prevalence of chromosomal aberrations related to translocation was 4.5 times higher in Reciprocal carrier group than in Robertsonian translocation carrier group. Among maternal and paternal carrier groups, the embryos from female carriers had the lowest euploidy rate, unbalanced translocation rate 4.7 times higher than in the male carrier group and higher total aneuploidy rates.

Time-lapse imaging reveals delayed development of embryos carrying unbalanced chromosomal translocations

PURPOSE

The purpose of the study was to compare the morphokinetic parameters of embryos carrying balanced chromosomal translocations with those carrying unbalanced chromosomal translocations using time-lapse microscopy.

METHODS

The study group included 270 embryos that underwent biopsies on day 3 for preimplantation genetic diagnosis (PGD) for chromosomal translocations in our unit between 2013 and 2015. All embryos were incubated under time-lapse microscopy and evaluated for timing of developmental events up to day 5. The timing of these events was compared between balanced and unbalanced embryos, potentially viable and nonviable variants, and maternal versus paternal inheritance of the translocation.

RESULTS

The PGD analysis found that 209 (77%) of the 270 biopsied embryos carried an unbalanced translocation. Embryos carrying unbalanced translocations, which are expected to lead to implantation failure or miscarriage, cleaved less synchronously and were delayed in time of cleavage to the 4-cell stage (t4) and in time of start of blastulation (tSB) compared with balanced embryos (P < 0.05). Furthermore, embryos carrying nonviable translocations demonstrated a significant delay at the time of pronuclei fading (tPNf) compared with those carrying potentially viable translocations (P < 0.05). Embryos whose unbalanced translocations were of maternal origin were significantly delayed in most of the morphokinetic parameters (including tPNf, t2, t3, t4, t6, t7, t8, cc2, s2, and tSB) compared with embryos carrying balanced translocations (P < 0.05).

CONCLUSIONS

Embryos carrying unbalanced chromosomal translocations mainly of maternal origin undergo delayed development and asynchronous cleavage that may lead to implantation failure or miscarriage.

Preimplantation genetic diagnosis and screening: Current status and future challenges

Preimplantation genetic diagnosis (PGD) is a clinically feasible technology to prevent the transmission of monogenic inherited disorders in families afflicted the diseases to the future offsprings. The major technical hurdle is it does not have a general formula for all mutations, thus different gene locus needs individualized, customized design to make the diagnosis accurate enough to be applied on PGD, in which the quantity of DNA is scarce, whereas timely result is sometimes requested if fresh embryo transfer is desired. On the other hand, preimplantation genetic screening (PGS) screens embryo with aneuploidy and was also known as PGD-A (A denotes aneuploidy) in order to enhance the implantation rates as well as livebirth rates. In contrasts to PGD, PGS is still under ferocious debate, especially recent reports found that euploid babies were born after transferring the aneuploid embryos diagnosed by PGS back to the womb and only very few randomized trials of PGS are available in the literature. We have been doing PGD and/or PGS for more than 10 years as one of the core PGD/PGS laboratories in Taiwan. Here we provide a concise review of PGD/PGS regarding its current status, both domestically and globally, as well as its future challenges.