Ageing eggs: Do we really need to freak out?

parent's age can affect children's age
Image by Azoreg via Wikimedia Commons

Yes and no. Women used to be told that we had to have babies by age 30. Now we are told by age 35 is okay. The age at which we choose to have children can affect the health, ageing and life span of our children. The same goes for us. The age our parents were when we were born can affect our health and life span. But it is a really complicated interplay between genes and environment. Basically younger parents have healthier genes, but older parents can often provide a better environment. And it isn’t clear which is more important. Also how long your parents live is more important than how old they were when they had you. If your parents live to be 100, there’s a good chance you will too.

It’s not all bad news for older parents. A recent study showed that kiwi mums over 35 had taller and slimmer children than younger mothers. Older parents often have more money than younger parents, are more educated and make healthier lifestyle choices: less parties, more salad and exercise. This can have a dramatic effect on the health of children. Many studies have shown that what parents eat (yes fathers too) can affect the DNA of their children, grandchildren and great grandchildren (as if pregnant women didn’t need any more pressure!). Diet affects offspring through epigenetics: changes in chemical marks on DNA, without actually altering the DNA structure.

But there a few reasons why it is a good idea to have your babies earlier rather than later. The biggest one is that the older you are, the harder it may be to conceive. Unlike men, who make sperm throughout their life, women have all their eggs made before we are even born. By the time we are 30, we have lost about 90% of the eggs we were born with. Also the reproductive cycle is controlled by hormones. Hormone levels change as we get older making it harder to conceive and to maintain a healthy pregnancy.

The second big reason is that older eggs are more likely to have damaged DNA. All cells accumulate DNA damage as they age. So an older egg may have developed a mutation which prevents it from developing into a healthy baby. DNA damage can roughly be divided into three main types: chromosomal abnormalities, nuclear DNA mutations and mitochondrial DNA mutations. A chromosomal abnormality is where a whole chromosome is either not copied or is copied twice. Chromosomal abnormalities can result in diseases like Down’s Syndrome, but most often cause early miscarriage.

Almost all of our DNA is kept in the nucleus of cells. This provides a template to make all the proteins that a cell needs to survive and function properly. Damage to this DNA may cause a disease-causing mutation. Diabetes and Huntington’s are examples of diseases caused by mutations in nuclear DNA.

Mitochondria are organelles inside all cells that produce the energy needed for the cell to function. Mitochondria are so important that they have their own DNA. One copy of nuclear DNA is inherited from each parent. Mitochondria and mitochondrial DNA only come from the mother. Mitochondria produce energy through a series of chemical reactions which produce damaging by-products. So the DNA in mitochondria is particularly prone to damage. Therefore older eggs may have mitochondria which don’t work efficiently and so have a hard time producing the massive amount of energy that is needed to produce a human baby.

Pregnancy, childbirth and looking after a tiny baby is a hugely emotional, wonderful and difficult experience. I don’t think women should let the scientific literature scare us into having babies before we are ready. We should just make sure to be as healthy as possible leading up to and during pregnancy.

The Scientific Papers:
Wildling et al. Maternal non-Mendelian inheritance of a reduced lifespan? A hypothesis. J Assist Reprod Genet. 2014
Savage et al. Increasing Maternal Age Is Associated with Taller Stature and Reduced Abdominal Fat in Their Children. Plos One 2013.
Wildling. Can we define maternal age as a genetic disease? Facts Views Vis Obgyn. 2014

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