Chromosomal abnormalities in oocytes

Since the beginning of in vitro fertilization (IVF), basic research has pro vided insight in the field of human reproduction, especially in genetics. I ndeed. the contribution of chromosomal abnormalities to oocyte disorders an d impaired embryonic development is now well known. Of oocytes that fail to fertilize after in vitro insemination, 26.5% have been found to be abnorma l. with 13.3% showing hypohaploidy, hyperhaploidy, 1.6% structural abnormal ities and 3.5% diploidy. The total incidence of abnormalities seems to be c orrelated with the fertility status of the woman, It is higher in oocytes f rom women with tubal or unexplained infertility than in those from women wh ose husband's infertility is the sole cause of infertility in the couple. A lthough few oocytes recovered during natural cycles have been studied, gona dotropins, which are widely used to stimulate follicle growth and ovulation , do not increase the risk of abnormalities. The effect of maternal age on fetal aneuploidy, well documented at birth, has not been unambiguously show n to result from an increase in the frequency of aneuploid oocytes. Intra- and extra-follicular influences (perifollicular micro asculature, oxygenati on, and the presence of residues from cigarette smoke) may disturb maturati on. leading to immaturity and aneuploidy. Thus, oocyte meiosis is very sens itive to endogenous and exogenous factors that could result in oocytes with chromosomal abnormalities and therefore. abnormal zygotes. (C) 2001 Elsevi er Science Ireland Ltd. All rights reserved.