Chromosomal Preparations from Human Oocytes

It appears that the chance of an in vitro fertilization (IVF) embryo to produce a pregnancy carried to term is about 10%.1 Consequently, one of the most important factors in increasing the pregnancy rate after in vitro fertilization and embryo transfer is replacement of multiple embryos.2 When we consider that the estimated human fecundity rate is about 25%,3 it seems likely that the quality of the embryo is one determining factor for a successful pregnancy rate. Different types of defects of gametes and embryos might contribute to the explanation of why the vast majority of IVF embryos do not give rise to any sign of pregnancy after replacement. It is well documented that chromosomal abnormalities among first trimester spontaneous abortions occur at a rate of about 60%, indicating that chromosomal abnormalities might be common in human gametes and early development stages.4 Abnormal karyotypes found were aneuploidy (i.e., complements with one extra or one missing chromosome) and polyploidy. Recently, a new technique allowing direct analysis of the chromosomal constitution of human spermatozoa has been reported.5 This technique utilizes the ability of capacitated human spermatozoa to penetrate zona-free hamster oocytes. Five to 10% of penetrating human spermatozoa have shown chromosomal abnormalities. Various degrees of hyperploidy and hypoploidy ranging from three extra to three missing chromosomes were found in a series of 1000 human spermatozoal chromosome constitutions.6 It is interesting to note that among spontaneous first trimester abortions such serious numerical abnormalities have not been found.4