P-146 The importance of cytoplasmic strings between inner cell mass and trophectoderm after blastulation on embryonic development and pregnancy outcome
Authors: Zhu J , Han W , Huang G 
Published: July 2024

Abstract

Study question
Whether the cytoplasmic strings between inner cell mass and trophectoderm during blastocyst expansion have a significant impact on embryo development and pregnancy outcomes?

Summary answer
The presence of cytoplasmic strings is related to morphological quality, but it has no impact on embryo ploidy or clinical outcome after euploid embryo transfer.

What is known already
Cytoplasmic strings are a dynamic cellular structure, and their width and length vary with the degree of embryonic expansion. The presence of cytoplasmic strings is considered a characteristic of embryos with poor vitality. In recent years, researchers have found the presence of cytoplasmic strings may indicate a higher embryonic developmental potential. However, the specific function of cytoplasmic strings remains unclear, and their impact on embryonic development is still controversial.

Study design, size, duration
A retrospective cohort analysis was conducted on clinical data of 530 patients who underwent single blastocyst transfer after pre-implantation genetic testing for aneuploidy (PGT-A) in our center from June 2019 to December 2021. Two embryologists annotated the presence of cytoplasmic strings, the morphological quality of blastocyst.

Participants/materials, setting, methods
A total of 2132 biopsied blastocysts were obtained from the 530 patients, with 534 blastocysts having cytoplasmic strings (+) and 1598 blastocysts having cytoplasmic strings (−). The quality and ploidy differences between the two groups were compared. After PGT-A, single euploid blastocysts were transferred, and the difference in pregnancy outcomes between cytoplasmic strings (+) (n = 115) and cytoplasmic strings (−) (n = 415) cycles was compared.

Main results and the role of chance
There was no significant difference in the euploidy rate between the two groups (44.6% vs. 45.3%). As the morphological quality of the embryos decreased, the rate of cytoplasmic strings (+) significantly decreased (Good-quality vs. Average-quality: 30.19% vs. 24.62%, P = 0.008; Average-quality vs. Low-quality: 24.62 vs. 12.63, P = 0.000). After adjusting for patient age, anti-Müllerian hormone, and gonadotropin dose, multivariate regression analysis showed that cytoplasmic strings were associated with embryo quality, but not with embryo ploidy. There were no significant differences in implantation rate (72.17% vs. 66.02%, P = 0.213), miscarriage rate (10.43% vs. 8.43%, P = 0.504), and live birth rate (61.74% vs. 57.59%, P = 0.424) between blastocysts with cytoplasmic strings (+) and without cytoplasmic strings (−).

Limitations, reasons for caution
Larger datasets are required to confirm putative associations between cytoplasmic strings and blastocyst ploidy, and the pregnancy outcome.

Wider implications of the findings
The presence of cytoplasmic strings is related to the embryological quality of the blastocyst, but it has no impact on embryo ploidy or clinical outcome after euploid embryo transfer.

Trial registration number
not applicable