Sperm retention site and its influence on pronucleus stage evaluation following intracytoplasmic sperm injection

Abstract

Aim: It has been suggested that the position of the sperm after intracytoplasmic sperm injection (ICSI) has an effect on the development and quality of the embryo. In this study, we retrospectively examined whether pronucleus stage evaluation used through clinical studies in recent years has relevance with regard to sperm location. Methods: From 2003 to 2005, 1285 oocytes from 459 patients (average age: 36 years) were retrospectively analyzed. The 459 patients underwent ICSI because of fertilization disorders and oligozoospermia. Follicle stimulation was via either Clomid or the long protocol. Human chorionic gonadotropin was administered to induce ovulation and oocyte retrieval was conducted 35 h later. After confirming the presence of a polar body, we immobilized the ovum at the 6 o'clock position, introduced the injection pipette at the 3 o'clock position and carried out ICSI. Results: When a sperm was located at a position that was opposite to the polar body, both classifications of Scott and Tesarik regarding embryo quality were distinctly low. Furthermore, a good embryo classification ensued when the sperm was located adjacent to the polar body. Conclusion: The zone in which the sperm was located did not always correlate with embryo quality; however, our study suggested that sperm location affects the synchronization of the nucleolus. When carrying out ICSI, it is important to take into consideration the insertion point of the sperm. © 2007 The Authors Journal compilation © 2007 Japan Society for Reproductive Medicine.