It’s well understood that women have a more and more difficult time becoming pregnant as they move past 30, 35, or 40 years of age. But the menstrual cycle keeps on ticking off the months, and menopause typically doesn’t arrive until a woman’s late 40’s or early 50’s.
Assuming the menstrual cycle is still happening, why might an aging woman have a harder time becoming pregnant than she would have 10-15 years earlier? Assume for the sake of this discussion that the male with whom she’s trying to conceive is contributing an adequate quantity of healthy sperm.
Is there actually no egg being released that month, despite the menstrual activity?
Do the sperm have difficulty reaching the egg due to changes in the uterine environment?
Does the zygote have trouble implanting in the uterus?
Possibly the age of the egg is the problem. In my Bio 101 class last year we learned that the human body produces all its eggs by a certain age but they don’t undergo their final division until their turn to be released. So, the earlier a woman gets pregnant, the younger and healthier her eggs are. But as she gets older, the eggs get older and more decrepit and may not divide properly (leading to more birth defects as well as infertility).
That is a very basic summary of what it said in my text and is only one possible reason for infertility in older women.
Since this was a community college, the vast majority of the women in the class were older than me (I’m 32) so my professor suggested that if any of us were considering having babies at a later age, it would be a good idea to undergo testing to determine the health of the remaining eggs.
Here’s a more technical explanation of what I said:
“Meiosis occurs repeatedly in a human lifetime as the testes or ovaries produce gametes. Almost always, the meiotic spindle distributes chromosomes to daughter cells without error. But, there is an occasional mishap, called nondisjunction, in which the members of a chromosome pair fail to separate.”
“Nondisjunction explains how abnormal chromosome numbers came about, but what causes nondisjunction in the first place? We do not yet know the answer. We do know, however, that meiosis begins in a woman’s ovaries before she is born but is not completed until years later, at the time of an ovulation. Because only one egg cell usually matures each month, a cell might remain arrested in the mid-meiosis state for decades. Some research points to an age-dependent error in one fo the checkpoints that coordinates the process of meiosis.”
Both those quotes came from Biology Concepts and Connections 6th edition.
Anyway, nondisjunction can cause birth defects (the common example in the text is trisomy 21 - Down Syndrome - which causes a daughter cell with 3 alleles on the 21st chromosome and a daughter cell with one allele on the 21st chromosome instead of 2 daughter cells each with 2 alleles on the 21st chromosome. The daughter cell with 1 allele would most likely cause an nonviable pregnancy and the one with 3 alleles would most likely cause a baby with Down syndrome - assuming they are successfully fertilized and implanted.
So, if the cells aren’t dividing properly and are causing birth defect causing or nonviable cells, then the woman will have a hard time getting pregnant and maintaining a pregnancy which produces a healthy baby.
It has to do with the quality of the eggs. A woman does not produce new eggs so they are effectively as old as she is. Many of these older eggs are abnormal.
This is actually what I research - or at least it’s tangentially related. The reasons for age-related increases in nondisjunction are only know beginning to be understood. Part of the problem is sister chromatid cohesion, which holds the homologous chromosomes together. Let’s back up.
When a woman in still in the womb, all of her eggs begin to go through meiosis. They halt at a stage where homologous chromosomes (that is, her maternal #1 and paternal #1, maternal #2 and paternal #2, etc, etc) are stuck together by a molecule called cohesin (actually a complex of at least four proteins). Conventional wisdom for years has been that cohesin is loaded onto the chromosomes early on, while still in the womb, and those individual protein molecules have to hang out for decades. If cohesion is lost, nondisjunction rates increase, which is what is seen in older mothers. So the idea has been that over time, these cohesin molecules are just gradually lost, leading to higher NDJ rates.
We’re beginning to see that it’s more complicated than that. It turns out that mechanisms to exist to reestablish cohesin molecules over time. How exactly that works in humans and why it seems to stop working in older women still remains to be explained. But we’re working on it.
This article doesn’t prove the theory is inaccurate. They need to see if the results can be replicated. They’re not even sure whether these new eggs are viable.
My understanding is that for women over 40, IVF with donor eggs is much more successful than IVF with the woman’s own eggs. That is strongly suggestive that the primary problem is in the eggs, not the womb or the mechanics of conception.
It also doesn’t say anything about the how these cells act in the human body. They haven’t shown any evidence of new eggs being formed in the human body after birth, only that certain cells can be coaxed to develop under laboratory conditions. Not all that surprising to be honest. Definitely not proof that the theory is inaccurate.
In real life, that’s probably also an invalid assumption.
In most cases, a woman in her 30’s, 40’s or 50’s has a husband of similar age. So the quality & quantity of sperm produced by a man in his 30’s, 40’s or 50’s is inferior to that of a younger man, of normal fatherhood age.
So by their 30’s, 40’s or 50’s, both of the parents are working with degraded materials, and so at a bit of a disadvantage for conceiving.
Yes; the eggs start to deteriorate; work is happening to look for ways to keep them viable longer. IANAFertilty doc, but work with them (smeghead, where are you based? Love the username in this context).
