Ultrastructure of tubular smooth endoplasmic reticulum aggregates in human metaphase II oocytes and clinical implications

Abstract

Objective: To compare demographic, embryologic, pregnancy, and newborn outcomes after intracytoplasmic sperm injection (ICSI) cycles with or without mature oocytes (metaphase II [MII]) showing visible aggregates of tubular smooth endoplasmic reticulum (aSERT) and to describe the ultrastructure of this dysmorphism.

Design: Retrospective study.

Setting: Private fertility center and university cell biology and genetics departments.

Patient(s): There were 721 ICSI cycles, 520 carrying morphologically normal MII (control group) and 60 containing aSERT-MII (study group).

Intervention(s): None.

Main outcome measure(s): Embryologic and clinical and live birth outcomes, including malformations and ultrastructural characterization of aSERT-MII.

Result(s): Compared with the control group there was a significant decrease in the fertilization, embryo cleavage, and blastocyst rates in the study group. The only child born after transfer of embryos derived from aSERT-MII presented a major cardiovascular malformation. Ultrastructurally, large aSERT were surrounded by abnormal-shaped mitochondria and clusters of small dense bodies formed by very small vesicles, and they had curvilinear dense tubules in the interior. The same pathology was observed in small peripheral aSERT.

Conclusion(s): The presence of large aSERT, showing attainment of the periphery, demonstrated that the cytoplasm is pathologic. The compromised embryo development and implantation was associated with decreased clinical outcomes and newborn malformations. Therefore, oocytes with large aSERT should not be used for embryo transfer.