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Spatiotemporal perturbations of pronuclear breakdown preceding syngamy affect early human embryo development: a retrospective observational study

  • Embryo Biology
  • Published:
Journal of Assisted Reproduction and Genetics Aims and scope Submit manuscript

Abstract

Purpose

During fertilisation, female and male pronuclei (PNs) migrate to the centre of the ooplasm, juxtapose, and break down synchronously in preparation for the first mitosis. While PN non-juxtaposition and PN breakdown (PNBD) asynchrony are occasionally observed, their developmental implications remain uncertain. This study investigated the possible relationships among the two phenomena, preimplantation development patterns, and live birth rates in single blastocyst transfers.

Methods

A total of 1455 fertilised oocytes cultured in a time-lapse incubator were retrospectively analysed. Fertilised oocytes were divided into four groups according to the presence of PN juxtaposition and breakdown synchrony. The relationships of abnormal PN behaviour with embryo morphokinetics, blastocyst formation, and live birth were evaluated.

Results

PN non-juxtaposition and asynchrony were observed in 1.9% and 1.0% of fertilised oocytes, respectively. The blastocyst cryopreservation rates in the synchronous–non-juxtaposed and asynchronous–non-juxtaposed groups were significantly lower than that in the synchronous–juxtaposed group. The rates of clinical pregnancy, ongoing pregnancy, and live birth were comparable among the groups. Non-juxtaposition was significantly associated with increased trichotomous cleavage at the first cytokinesis (P < 0.0001) and an increase in the time interval from PNBD to first cleavage (P < 0.0001). Furthermore, asynchronous PNBD was significantly correlated with increased rapid cleavage at the first cytokinesis (P = 0.0100).

Conclusion

Non-juxtaposition and asynchronous PNBD is associated with abnormal mitosis at the first cleavage and impaired preimplantation development. However, embryos displaying abnormal PNBD may develop to blastocyst stage and produce live births, suggesting blastocyst transfer as a more appropriate culture strategy.

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Abbreviations

AJ:

asynchronous–juxtaposed

AN:

asynchronous–non-juxtaposed

CC:

clomiphene citrate

FSH:

follicle-stimulating hormone

hMG:

human menopausal gonadotropin

HTF:

human tubal fluid

ICM:

inner cell mass

ICSI:

intracytoplasmic sperm injection

NPB:

nucleolus precursor body

PN:

pronuclei

PNBD:

pronuclei breakdown

rFSH:

recombinant follicle-stimulating hormone

SJ:

synchronous–juxtaposed

SN:

synchronous–non-juxtaposed

SVBT:

single vitrified-warmed blastocyst transfer

t2:

two-cell stage

t3:

three-cell stage

TE:

trophectoderm

tHa:

time of halo initiation

tHd:

time at which the halo phenomenon disappeared

tHr:

time at which the granules started to redistribute

TI:

time interval

tPB2:

second polar body

tPN1:

the appearance of the first PN

tPN2:

the appearance of the second PN

tPNf:

pronuclei fading

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Availability of data and material

The primary data for this study are available from the authors on direct request.

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Author information

Authors and Affiliations

  1. Kato Ladies Clinic, 7-20-3 Nishishinjuku, Shinjuku-ku, Tokyo, 160-0023, Japan

    Kenji Ezoe, Hitomi Takenouchi, Shota Taoda, Shima Namerikawa, Kasumi Honda, Tetsuya Miki, Tadashi Okimura, Tamotsu Kobayashi & Keiichi Kato

  2. 9.Baby, Family and Fertility Center, Via Dante 15, 40125, Bologna, Italy

    Giovanni Coticchio & Andrea Borini

Authors
  1. Kenji Ezoe
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  2. Giovanni Coticchio
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  3. Hitomi Takenouchi
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  6. Kasumi Honda
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Contributions

Kenji Ezoe designed the study; Kenji Ezoe, Hitomi Takenouchi, Shota Taoda, Shima Namerikawa, Kasumi Honda, and Tetsuya Miki observed and annotated embryo development; Kenji Ezoe analysed the data; Kenji Ezoe, Giovanni Coticchio, and Keiichi Kato wrote the paper; Tadashi Okimura, Tamotsu Kobayashi, and Andrea Borini revised the paper.

Corresponding author

Correspondence to Keiichi Kato.

Ethics declarations

Ethics approval

The study was approved by the Institutional Review Board of the Kato Ladies Clinic (approval number: 16-32).

Consent to participate

Written informed consent for the retrospective analysis of de-identified data was obtained from patients undergoing in vitro fertilisation treatment at the centre.

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Not applicable.

Conflicts of interest

The authors declare no competing interests.

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Supplementary information

Fertilised oocyte that exhibited pronuclei non-juxtaposition and synchronous pronuclei breakdown (WMV 12917 kb)

Fertilised oocyte that exhibited pronuclei juxtaposition and asynchronous pronuclei breakdown (breakdown) (WMV 14147 kb)

Fertilised oocyte that exhibited pronuclei juxtaposition and asynchronous pronuclei breakdown (shrinkage) (WMV 13009 kb)

Fertilised oocyte that exhibited pronuclei non-juxtaposition and asynchronous pronuclei breakdown (WMV 14735 kb)

ESM 5

Supplementary information Table 1 Embryonic outcomes stratified by the patient and characteristics of pronuclei behaviour. Supplementary information Table 2 Multivariate logistic regression analysis for pregnancy outcomes in embryos with anomalies in pronuclei breakdown. Supplementary information Table 3 Embryonic outcomes of fertilised oocytes with non-juxtaposition, stratified by the distance between two pronuclei. Supplementary information Table 4 Embryonic outcomes of fertilised oocytes with asynchronous pronuclei breakdown, stratified by the time intervals of pronuclei breakdown asynchrony. (DOCX 48 kb)

Fig. S1

Flowchart describing the method of patient selection, including inclusion and exclusion criteria. Women who previously underwent embryo transfer four or more times were defined as experiencing recurrent implantation failure (PNG 136 kb)

High resolution image (TIF 204 kb)

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Ezoe, K., Coticchio, G., Takenouchi, H. et al. Spatiotemporal perturbations of pronuclear breakdown preceding syngamy affect early human embryo development: a retrospective observational study. J Assist Reprod Genet 39, 75–84 (2022). https://doi.org/10.1007/s10815-021-02335-6

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  • DOI: https://doi.org/10.1007/s10815-021-02335-6

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