P-545 The age-related required number of zygotes estimated from prior clinical studies of preimplantation genetic testing for aneuploidy (PGT-A)

Study question

How many eggs will be required to optimize the chances of a live birth with or without PGT-A?

Summary answer

The number of zygotes required for live birth is higher in women with an advanced age, and the use of PGT-A does not provide improvement.

What is known already

Women who are undergoing PGT-A often wish to know how many eggs will be required to optimize the chances of a live birth. This important information could be provided as part of prior genetic counseling, but there are no precise data on this at present. If the number of eggs required to give the best chance of a successful live birth was known, treatment plans with or without PGT-A could be better determined.

Study design, size, duration

We estimated the optimal number of eggs required for IVF treatment with PGT-A to produce at least a single live birth, stratified by maternal age, on the basis of information from prior studies and in current databases.

Participants/materials, setting, methods

We derived our calculation parameters from three prior large-scale clinical investigations associated with PGT-A. We estimated a live birth rate using the following factors: rate of zygotes that develop a useful blastocyst, euploid rate in PGT-A, and the live birth rate after euploid embryo transfer. All of these factors were assumed to be statistically independent in this study for the purposes of our calculations and the live birth rate per single zygote was calculated.

Main results and the role of chance

The estimations in our present analyses however indicate a probability of less than 10% that woman over 40 years of age will have a live birth from a single zygote, regardless of whether PGT-A is performed or not. We used a negative binomial distribution approach to calculate how many zygotes are needed to obtain at least one live birth. The plot of these results is provided in Figure 2. To achieve a 50% chance of getting at least one live birth, patients required 8 zygotes at age of 40 and 21 zygotes at the age of 43. Furthermore, to achieve an 80% chance of obtaining a live birth, our calculations estimate that 18 and 47 zygotes would be required at these two ages, respectively, which would be challenging to achieve. On the other hand, by avoiding unnecessary transplants using PGT-A, women may have to wait a shorter period to accomplish a live birth or may be able to avoid wasting their limited remaining reproductive period, particularly if they are older than 42.

Limitations, reasons for caution

The reference data from PGT-A studies that have estimated of the live birth rate include chromosomal quantitative PCR, microarray analysis, and next generation sequencing (NGS). There is a high possibility that the embryos designated as “euploid” in those studies include mosaic embryos, which represents a limitation of our present meta-analysis.

Wider implications of the findings

More details on the clinical outcomes of PGT-A will be revealed as clinical studies progress in the future. It is our hope that the results of this present study will assist with future genetic counseling strategies for PGT-A in the meantime.

Trial registration number

not applicable

P-131 The fate of irregularly divided blastomeres: why does “Direct cleavage” reduce blastocyst development rate but not blastocyst euploid rate?

Study question

How do the blastomeres formed by direct cleavage (dynamics of one cell dividing into three or more cells) subsequently develop?

Summary answer

About half of the blastomeres by direct cleavage did not form blastocysts.

What is known already

There are many reports that embryos with direct cleavage in the early development have a lower blastocyst development rate because direct cleavage produces chromosomal abnormal cells. However, when such embryos develop into blastocysts, there have been some reports that the transfer pregnancy rate and euploid rate did not decrease, but the reasons for this have not been clarified.

Study design, size, duration

This is a retrospective study of 89 blastocysts obtained during 2013-18. These embryos were those that patients requested to be discarded and consented to be used in this study. All target embryos were time-lapse monitored by EmbryoScope (Vitrolife, Sweden), and several trophectoderms were biopsied and examined for euploidy.

Participants/materials, setting, methods

The target embryos were classified into three groups: embryos with normal first and second cleavage (NC group), embryos with irregular division (one cell dividing into three or more cells) called direct cleavage at the first cleavage (DC1 group), and embryos with direct cleavage of one blastomere at the second cleavage (DC2 group). It was recorded whether the blastomeres of the embryos subsequently developed into blastocysts or not. NGS analysis was performed on the embryos.

Main results and the role of chance

The target embryos were classified as 48 in the NC group, 32 in the DC1 group, and 9 in the DC2 group. Whether the blastomeres in the target embryos subsequently formed blastocysts or not was recorded one by one by time-lapse images, resulting in the blastomeres’ blastocyst formation rate was 95.1% in the NC group and 55.9% in the DC1 group, which was significantly lower in the DC1 group (P < 0.01). In the DC2 group, blastomeres formed by normal division and those by direct cleavage at the second cleavage were recorded separately, and the blastocyst formation rate was 90.8% for normal cleavage blastomeres and 46.0% for direct cleavage blastomeres, with significantly lower rates for direct cleavage blastomeres (P < 0.01). Therefore, about half of the blastomeres generated by direct cleavage at the first or second cleavage did not form blastocysts. The results of NGS analysis were as follows: NC group: 35.4% euploid, 45.8% aneuploid, and 18.8% mosaic; DC1 group: 37.5%, 53.1%, and 9.4%, respectively; and DC2 group: 55.6%, 33.3%, and 11.1%, respectively. There was no significant difference in any of the items, suggesting that direct cleavage does not affect the euploidy of blastocysts.

Limitations, reasons for caution

For the purpose of NGS analysis, all the target embryos in this study were blastocysts, but if all the cultured embryos were included, arrested embryos would be included, which would probably result in more blastomeres formed by direct cleavage not developing into blastocysts.

Wider implications of the findings

The blastomeres generated by direct cleavage were often excluded from blastocyst formation. This may be an exclusion of chromosomally abnormal cells and may be one of the reasons why direct cleavage decreases blastocyst development rate but does not decrease blastocyst euploid rate.

Trial registration number

not applicable

Are folliculo-stellate cells in the anterior pituitary gland supportive cells or organ-specific stem cells?

Folliculo-stellate cells (FS-cells) in the anterior pituitary gland are star-shaped cells and form tiny follicles. FS-cells are positive for S-100 protein and produce many cytokines or growth factors, such as interleukin-6 (IL-6), leukemia inhibitory factor (LIF), basic fibroblastic growth factor (bFGF) and vascular endothelial cell growth factor (VEGF). Therefore, it is generally accepted that FS-cells regulate endocrine cells through these growth factors. FS-cells also exhibit a phagocytotic activity and are known to work as scavenger cells. In addition to these functions, FS-cells are considered to have some unknown functions. In order to reveal the biological significance of FS-cells in the anterior pituitary gland, we performed a morphological study and obtained some new findings. First, we were interested in the colloid formation in the senescent porcine pituitary gland. We analyzed the colloids and found that clusterin is a major protein in them. We also found that the accumulation of clusterin in the colloids is related to the phagocytotic activity of FS-cells. In our next study, we found that FS-cells have the potential to differentiate into striated muscle cells. From FS-cells show multi-potent cell character and other cytological evidence, we propose that FS-cells are candidate of organ-specific stem cells in the anterior pituitary gland.

An exonuclease activity associated with DNA polymerase I of Micrococcus radiodurans

An exonuclease activity is associated with one of three DNA polymerase in Micrococcus radiodurans. The nuclease activity co-sedimented with its DNA polymerase I of this bacterium on glycerol gradient centrifugation. Both activities show the same optimum pH and heat-inactivation kinetics. This nuclease hydrolyzes preferentially double-stranded DNA in an exonucleolytic manner from both ends of the duplex DNA. The products of hydrolysis are mostly deoxyribonucleoside 5'-monophosphate and no nucleosides are released into the acid-soluble fraction. Di- or other oligonucleotides are also produced but their relative amounts are constant during the time of incubation. The exonuclease activity requires Mg2+ and is inhibited by high concentrations of KCl as is DNA polymerase I of M. radiodurans.