P-132 Outcomes of blastocyst transfer derived from oocytes with smooth endoplasmic reticulum clusters (sERC)
Authors: Takahashi H , Hirata R , Habara T , Hayashi N 
Published: July 2024

Study question

Are blastocysts derived from oocytes with smooth endoplasmic reticulum clusters (sERC+) as suitable for transfer as those from oocytes without such clusters (sERC-)?

Summary answer

Blastocysts from sERC+ oocytes are considered for embryo transfer; however, it is recommended to prioritize them lower than those from sERC- oocytes.

What is known already

One of the cytoplasmic abnormalities in human oocytes, sERC, typically manifests during the MII stage oocytes and disappears after fertilization when the female and male pronuclei emerge. Despite this, the mechanism behind sERC development remains unclear. While it is suggested that sERC in oocytes may adversely impact embryo development and implantation, a definitive conclusion on its safety or use has not been reached. Although the 2011 Istanbul consensus discouraged injecting or inseminating sERC+ oocytes, a 2017 expert panel reconsidered this recommendation, advocating for a case-by-case approach. Therefore, there are widespread variations in responses to sERC in clinical practices.

Study design, size, duration

A retrospective review of intracytoplasmic sperm injection (ICSI) cycles between April 2014 and April 2023 was conducted, exclusively on single frozen blastocyst transfers of two pronuclei (2PN)-derived embryos performed before June 2023. A dataset comprising 95 blastocysts from sERC+ oocytes and 8,698 blastocysts from sERC- oocytes was assembled. To reduce bias between groups, maternal age at retrieval and transfer counts were matched in a 1:1 ratio using propensity score matching, yielding 95 comparable cycle pairs.

Participants/materials, setting, methods

Among all ICSI cycles, 78 exclusively involved embryos from sERC+ oocytes, 847 included embryos from both sERC+ and sERC- oocytes, and 6,599 had no embryos derived from sERC+ oocytes. Among the 8,698 sERC- blastocysts transferred, 1,083 and 7,615 originated from cycles with and without sERC+ oocytes, respectively. Implantation, miscarriage, and live birth rates were then compared in 95 matched pairs of blastocysts derived from sERC+ and sERC- oocytes.

Main results and the role of chance

Following propensity score matching adjustments, the mean patient age at retrieval (mean ± SD) for blastocyst transfers derived from sERC+ and sERC- oocytes were 38.6 ± 4.7 years and 38.7 ± 4.8 years, respectively (p = 0.927). The transfer counts were 4.2 ± 3.4 times for sERC+ and 4.1 ± 3.1 times for sERC- blastocyst transfers (p = 0.840). The proportion of high-quality blastocysts was 48.4% for sERC+ transfers and 54.7% in sERC- transfers (p = 0.384). The implantation rates were 24.2% for sERC+ and 32.6% for sERC- transfers (p = 0.198), miscarriage rates were 43.5% vs. 35.5% (p = 0.552), and live birth rates were 13.7% vs. 21.1% (p = 0.172), respectively, with no statistically significant differences. Thirteen live births from sERC+ blastocyst transfers were recorded, and no congenital abnormalities were observed.

Limitations, reasons for caution

This study exclusively centered on oocytes subjected to ICSI, and the inclusion criteria were restricted to embryos derived from sERC+ oocytes in accordance with clinic policy limitations. Preimplantation genetic testing was not performed on the majority of the transferred embryos.

Wider implications of the findings

No congenital abnormalities were observed in live births resulting from sERC+ derived blastocyst transfers. However, the limited number of embryo transfers involving sERC+ oocytes poses a constraint in drawing a definitive conclusion regarding the safety of embryos from sERC+ oocytes, and further data is required.

Trial registration number

non-clinical trials