Good Eggs (Embryo Quality Part 1)

Did you know that women are born with approximately 2,000,000 eggs?

By the time of their first period, this number is reduced to approximately 300,000 (Marcus and Brinsden 1996), and your egg numbers will continue to fall until menopause. 

Did you know that there is also an increase in the rate of the production of your ovaries to release an egg each month?  This increases from the age of 37.5 years until menopause.

You’re asking the question what does this mean?  This means that the likely hood of a normal good quality egg released each month reduces, there is a reduced number of overall eggs that will be released that have the ability to fertilise normally and it can also increase the rate of miscarriage.

A study by Marcus and Brinsden 1996, found that age in women was associated with decreased embryo viability, meaning the quality of the eggs and embryos that result in a baby reduces.

Embryo quality is influenced by the egg maturity when it is released from the ovary, and this is determined by the biology of the egg and the environment its produced in.

It is thought the lining of a women’s uterus isn’t the issue when she gets older and is trying to fall pregnant, but the quality of her eggs that are released each month are.

A review by Ziebe et al., 2001 found higher pregnancy rates in older women who used donated eggs from younger women, showing that age does relates to egg quality.

A study by Garrido et al., (2000), found women with endometriosis had lower quality eggs and embryos.  This is thought to be due to an increase in reactive oxidative species (ROS) in the fluid found in fallopian tubes. ROS is an unstable molecule that contains oxygen and easily reacts with other molecules in the cell, causing cell damage.

Embryo quality: Age and Miscarriage  

Embryos undergo a process during development called fragmentation, this is where parts of the developing embryo’s cell breaks off and are separate from the main body of the embryo.  This is a very common process but the degree of fragmentation determines the quality and development of the embryo.

A study by Ziebe et al., (2001) found there was no real difference in the fragmentation rate for women under the age of 40, but once they reached 40 and over, the embryo fragmentation rate rapidly increased and this correlated with a significant decrease in embryo implantation in women over 40.

A study by Ziebe et al., (2001) found embryos at days 2 & 3 of development that were transferred in women aged over 40, showed a significant decrease in implantation rate.

What does this mean? This means that even though the embryo grade and quality looked, to the naked eye, structurally as good as an embryo from a younger woman, there was a decrease in the embryo quality with an increase in the age of a women. 

Scientists have also documented that in day 5/6 embryos (Ahlstöm et al., 2011) as a woman gets older there is a decrease in quality of the embryo.

This leads to a lower percentage of embryos reaching the day 5/6 stage, and a decrease in the quality of embryos overall. With out taking a woman’s age into account, Ahlstöm et al (2011), found there was a greater chance of pregnancy with day 5 embryos that were the grading of 4BA or 3BA.

Embryo quality: Age and genetics  

As women age, their eggs begin to decrease in quality and quantity.  Women aged 37 years and over face a higher risk of embryos that have the incorrect genetic programming, such as Down’s syndrome and spontaneous miscarriage (Fleming and Cook 2008).  

In younger women, the structures within the egg cell are generally more normally organised at the developing egg stage.

Women aged 37 years and over have been found to experience more spontaneous miscarriages that are genetically abnormal (Ford 2013). 

According to a range of literature and studies, this is due to deterioration in the development process of the egg that occurs with age.  Ford (2013), found that women over 37 showed a decrease in some normal genetic structures in the egg.

Instances of Down’s syndrome have been found to increase with the age of both male and female partners. It is caused by an extra chromosome in the embryo (Yoon et al., 1996).  The extra chromosome that causes Down’s syndrome is approximately 80% from maternal origin and 20% paternal origin (Yoon et al., 1996). 

A woman aged around 20 years, the risk of Downs’s syndrome is 1/1667.   The risk increases to 1/30 around the age of 45 years (Heffner 2004). 

Allen et al., (2009) found in their large population-based study that there was a correlation between older women and the extra chromosome within the eggs. The study found there was a higher incidence of genetic errors for women ≥40 years of age at the time of their babies birth.  

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