Cytogenetic abnormalities of unfertilized oocytes generated from in-vitro fertilization and intracytoplasmic sperm injection: a double-blind study

Abstract

In the present study we have assessed the cytogenetic abnormalities of unfertilized oocytes from in-vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) programmes during a one year period (July 1995 to July 1996) with the cytogenetic analysis being carried out in a double-blind manner. A total of 88 unfertilized ICSI and 85 unfertilized IVF oocytes were used for the study and of these 51 and 62 oocytes, in each respective group, were suitable for analysis. The haploidy, diploidy and aneuploidy rates between ICSI (62.7, 7.8 and 5.9%) and IVF (61.3, 9.7 and 14.5%) groups were similar. A significant inter-patient variation in the incidence of hypohaploidy was observed within the IVF group. Chromosomal fragmentation or breakage was observed at a similar rate in both groups of unfertilized oocytes (23.5 and 14.5% for ICSI and IVF respectively). A significantly higher proportion of ICSI oocytes contained sperm nuclei (27/51, 52.9%) than did IVF oocytes (20/62, 32.3%, P < 0.01). The distribution and state of sperm head chromatin in relation to oocyte chromosomal complement was studied in both groups. ICSI oocytes contained decondensed or swollen sperm nuclei in association with haploid oocyte chromosomes (12/27, 44.4%) or condensed sperm heads in oocytes showing no chromosomal complements (7/27, 25.9%). In IVF oocytes sperm heads were either arrested in the condensed state (5/20, 25%), metaphase stage (3/20, 15%) or had undergone premature chromosome condensation (PCC; 6/20, 30%) in association with haploid oocyte chromosomes. The incidence of PCC was similar in the two groups. A marked variation in the incidence of total chromosomal abnormality was observed between patients within both ICSI (0-75%) and IVF (0-71%) groups indicating a possible similarity in oocyte quality between the majority of male factor and tubal infertility patients. The type of sperm used in the two fertilization procedures showed an increased incidence of chromosomal breakage with ICSI-MESA (microepididymal sperm aspiration) spermatozoa (4/6, 67%) compared to the ICSI-ejaculated (6/35, 17.1%; P < 0.05), ICSI-testicular biopsy (2/10, 20%) and IVF-normospermic (9/62, 14.5%; P < 0.01) spermatozoa. Chromosomal fragmentation may be associated with the degree of difficulty experienced at sperm injection, especially with sperm retrieved from the reproductive tract. Thus chromosomal fragmentation in ICSI may need further investigation using a larger sample size in order to assess the possible causative factors.