Chromosome analysis of single- and multipronucleated human zygotes proceeded after the intracytoplasmic sperm...

Fertilization of an egg by injection of a single spermatozoon into the cytoplasm has been shown to be an effective procedure to obtain a pregnancy in human in vitro fertilization. This, as one of the most invasive micromanipulation techniques, has generated concern about inducing embryo abnormalities. The objective of this study was to obtain insight into the chromosomal constitution of zygotes proceeded after the intracytoplasmic sperm injection procedure.

For this purpose the first cleavage division of 33 single- and 16 multipronucleated zygotes proceeded after the intracytoplasmic sperm injection procedure was cytogenetically analyzed.

Chromosome spreading permitted adequate karyotyping in 28 (84.8%) single-pronucleated zygotes. Among these, 19 (67.9%) were haploid, 5 (17.9%) hypohaploid (n = 20-22), and 4 (14.3%) hyperhaploid (n = 24-25). The overall rate of aneuploidy found here for single-pronucleated zygotes was 32.1%. In the 23 (82.1%) analyzed single-pronucleated zygotes, besides single mitotic complements, an intact sperm head or sperm nuclei structure has been found, indicating the maternal origin of these chromosomes.

Ten digynic zygotes with three pronuclei and six zygotes with more than three pronuclei were identified after injecting a single spermatozoon, representing 3.2% of all the fertilized oocytes. Aneuploid chromosome complements were found in three of seven tripronuclear zygotes and each one exhibited a hypo-, hyper-, and haploid complement (23,X, 21,X,-A,-B, 25,X, +A,+B; 23,Y, 22,X,-D, 24,X,+D; 23,X, 22,X,-G, 24,X,+G). The absolute difference in the number of chromosomes between each of these two imbalanced corresponding haplotypes was the same and this difference was caused by the chromosomes belonging to the same groups of karyotype. Of the remaining four tripronuclear zygotes, three had triploid and one had diploid numbers of chromosomes. Furthermore, five zygotes having more than three pronuclei at the first cleavage division displayed severely depleted chromosome complements. The majority of imbalanced multipronuclear zygotes was found after delay of the microinjection, suggesting that aging of oocytes might be the reason for their abnormal chromosomal arrangements.