A new study out of Montreal Hospital Research Center is providing a new explanation for why women’s fertility declines with age. The study compared the eggs of 6-12 week old mice to those of 60 week old mice. They found that the microtubules in older eggs behave abnormally. Microtubules help with chromosome segregation during cell division. In older eggs, the microtubules were found to go in all directions, instead of assembling a symmetric spindle as they are supposed to. When the microtubules don’t function normally, then cells may not end up with the correct number of chromosomes as the cells divide, leading to abnormal eggs.
We have known for a long time that genetically abnormal eggs are a large reason why women have more difficulty conceiving and a higher risk of miscarriage as they get older. It was previously thought that this was due to a problem with the “glue” that keeps the chromosomes together, which is known as the “cohesion-loss” hypothesis. The new information regarding the microtubules does not contradict this idea, but gives us information about the existence of another problem in older eggs.
For a fertility physician, seeing this type of research is exciting. It gives me hope that as we learn more about what causes fertility to decline as women get older, we can begin researching how to treat these problems. Unfortunately, this type of research will take time though, so treatments to correct chromosomal abnormalities in eggs are still a long ways off. For now, the best option we have for women who want to delay child-bearing until they are older is to freeze eggs for fertility preservation. Freezing eggs allows women to bank away eggs at a young age, before their microtubule function goes awry.
Fertility declines more rapidly after 35 years old. So, for any woman who is considering putting off pregnancy until their late 30’s or into their 40’s, I would recommend speaking with your physician about options for fertility preservation. This new research shows us why it’s important to be proactive about your future fertility.