• An abnormal number of chromosomes is referred to as aneuploidy
• Aneuploidy causes the increased rate of miscarriage with aging
• Aneuploidy is responsible for most of the decline in fertility with advancing age (both with and without IVF)

In recent years research has shown the importance of a structure in the egg called the meiotic spindle. This spindle is involved with aligning chromosome pairs so proper division of pairs can occur during egg maturation.

• As women age they are more likely to have an abnormal spindle apparatus that does not efficiently line up chromosomes prior to division
• This causes a higher likelihood for an unbalanced chromosomal situation in the mature egg – and then in the embryo

A recently published study (referenced below) might help us to understand why some women have more chromosomally abnormal eggs at a given age. This study was performed in mice, but may well have relevance for human reproduction as well (in many ways we aren’t as different from mice as we might like).

• The researchers identified a specific gene mutation in mice that is associated with a high rate of chromosomal abnormalities in the eggs and embryos
• The gene is called Bub1
• They showed that this gene is involved in regulation of division of pairs of chromosomes during egg maturation
• The severity of the chromosomal problems increased with age
• Because the chromosomal abnormalities were passed on to the resulting embryos, there were high rates of loss after embryo implantation

This could give us insight into reasons for some couples having infertility, repeated miscarriages, or repeated failures with in vitro fertilization. More research is needed in this area.

If humans are found to have a similar gene, it is possible that a blood test could be developed to see if women are at increased risk for having eggs and embryos with chromosomal abnormalities. Then fertility specialists could more accurately advise couples about effectiveness of available treatment options.

Reference for article discussed above:

S. Lelanda, et al: Heterozygosity for a Bub1 mutation causes female-specific germ cell aneuploidy in mice. PNAS August, 2009; Pages 12776-12781.

Links to related pages:

Eggs and chromosome problems

Age and fertility

IVF and age

Fertility and IVF in women after age 40

Egg donation

PGD, preimplantation genetic diagnosis: Should we test chromosomes of embryos?

Richard Sherbahn, MD is a fertility doctor practicing in the Chicago, Illinois area. Connect with me on Google+

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