Vitrification of human single pronuclear oocytes following two approaches to polar body biopsy

Abstract

The purpose of the present study was to investigate whether the size of the opening in the zona pellucida (ZP) of human single pronuclear (1PN) oocytes made by laser and partial zona dissection (PZD) techniques might interfere with the survival and subsequent development to blastocyst stage upon vitrification and warming. Moreover, the viability of these blastocysts was evaluated by comparing their total cell number (TCN) to the TCN of blastocysts developed from control non-vitrified zona-intact 1PN oocytes. Prior to vitrification, a total of 97 and 88 1PN oocytes were subjected to polar body biopsy using laser-assisted and PZD techniques, respectively. The size of ZP opening made by laser and PZD techniques did not interfere with survival (94.8% and 95.4%) or development to the blastocyst stage (27.8% and 26.1%). However, the TCN of laser-derived blastocysts was significantly lower than the TCN of blastocysts developed from non-vitrified control 1PN oocytes (48.7 ± 3.4 versus 70.8 ± 7.1, P < 0.028). The vitrification protocol used here is thus revealed to be an effective method for cryopreservation of 1PN oocytes following polar body biopsy. However, the viability of blastocysts developed from laser-treated 1PN oocytes seems to be negatively affected by this method of biopsy. The purpose of the present study was to investigate whether the size of the opening made in the outer membrane (zona pellucida) of human single pronuclear (1PN) oocytes by mechanical dissection and laser techniques followed by polar body removal could hamper survival and development to the blastocyst stage upon vitrification and warming. Vitrification is a simple method of cryopreservation in which the intra- and extracellular solutions transform during cooling into a solid, glass-like substance. Moreover, in order to predict the viability of blastocysts developed from vitrified 1PN oocytes, their total cell number (TCN) was recorded and compared with the TCN of blastocysts developed from non-vitrified zona-intact 1PN oocytes. Prior to vitrification, a total of 97 and 88 1PN oocytes were subjected to polar body biopsy using the laser-assisted and mechanical method of dissection, respectively. Vitrification was also applied to 61 zona-intact 1PN oocytes. Following vitrification, no disparity in survival or further development to blastocyst stage was observed between either of the two biopsied groups and zona-inact 1PN oocytes, revealing that the vitrification protocol used here is an effective method for cryopreservation of 1PN oocytes following polar body biopsy. However, the TCN of blastocysts developed from laser-treated 1PN oocytes was considerably lower than the TCN of blastocysts developed from non-vitrified zona-intact 1PN oocytes ( n = 46) suggesting that the viability of blastocysts developed from laser-treated 1PN oocytes was negatively influenced by this method of biopsy.