Structural abnormalities where there is a problem with the structure of a chromosome Examples include translocations, duplications and deletions of part of a chromosome

Aneuploid eggs and embryos are also responsible for most of the decline in overall fertility with female aging - and for the low pregnancy success rates with IVF for women over 40.

The increased rate of chromosomal abnormalities in women of advanced reproductive age has been well documented in research studies. The graph below shows the rate of chromosomally abnormal IVF eggs by female age. These numbers are approximate and compiled from several studies.

We do not know exactly why there is an increase in chromosomal abnormalities in the eggs of women as they age. However, research studies have clarified some of the issues involved.

The meiotic spindle is a critical component of eggs that is involved in organizing the chromosome pairs so that a proper division of the pairs can occur as the egg is developing. An abnormal spindle can predispose to development of chromosomally abnormal eggs.

An excellent study published in the medical journal "Human Reproduction" in October of 1996 investigated the influence of maternal age on meiotic spindle assembly in human eggs.

The pictures below are from this journal article. These photos were taken with confocal fluorescence microscopy of eggs stained with special dyes to show the spindles and chromosomes.

When the chromosomes line up properly in a straight line on the spindle apparatus in the egg, the division process would be expected to proceed normally so that the egg would end up with its proper complement of 23 chromosomes.

However, with a disordered arrangement on an abnormal spindle, the division process may be uneven - resulting in an unbalanced chromosomal situation in the egg.

Read the original here:
Female Age and Chromosome Problems in Eggs and Embryos

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