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Monday, 27 January 2014

Egg quality

In my last three blogs, I have attempted to shed light on how conception occurs and I am now moving on to the causes of why some people face difficulty in conceiving. For now I will focus on where it all starts, the ovary. For what happens normally, please refer to my earlier blog on role of ovary in conception. Please do feel free to ask questions on any aspect of fertility through the comment section below.

If we think logically, two things can go wrong at the ovary level. First, the egg is not of good quality and second, the egg is not released (or released infrequently). Let me talk about the first problem in this post. 

Poor egg quality is usually age related. The best eggs are recruited and released first and as age advances, the eggs that are released deteriorate in quality. What quality really implies is the competence to form an embryo with potential to implant and lead to a pregnancy. 

All our body cells have two copies of each chromosome (that carry the genetic information) and a total of 23 pairs of chromosomes. When an egg and a sperm unite the resulting embryo that will eventually grow into a baby should have a normal number of chromosomes. This can only happen if the egg and the sperms have reduced their chromosomes to one chromosome each of the 23 chromosomes. This is achieved through reduction division also called meiosis. The movement of the chromosomes is achieved with the help of a delicate structure called the meiotic spindle. The spindle is composed of an assembly of elastic threads arranged in an ellipsoid manner (with two poles or ends) and each thread pulls one chromosome towards one pole. The regulatory mechanisms responsible for the assembly of the spindle is altered significantly in older women and this leads to an increasing number of eggs with abnormal number of chromosomes (called aneuploidy), i.e. either one less or one more than the normal figure of 23. 

It has been estimated that the number of eggs that have an abnormal number of chromosomes is low (<10%) below the age of thirty-five, reaches 30% by age forty, 50% by forty-two and is almost 100% by the age of forty-five. This can explain the rise in the miscarriage rates and the incidence of abnormalities in the babies such as Down's Syndrome with increasing maternal age. It is for this reason that IVF with own eggs is very rarely successful after the age of 43yrs and hence IVF with donor eggs is recommended.

There is very limited that can be done to reverse this decline in egg quality and ovarian reserve. The latest medication which MAY help women with low ovarian reserve is DHEA (dehydroepiandrosterone). 

Ovulation disturbances in the next post....

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