Blog by Dr Andrew Murray
When parents of Generation X, the so-called “Baby Boomers”, started having children in the late 1960’s to early 70’s, the average fertility rate was around 3 children per couple, and the average age of mothers was 24. Now Gen X is having the kids and the fertility rate is less than 2 children per couple with the average age of mothers between 30 and 35.
The reasons for this are not hard to understand. More women are participating in tertiary education, many couples need double incomes, and to a certain extent we have been giving women the message from an early age “Girls can do Anything!” We are also living in a society where the norm has been to save for the house deposit, establish the career, and then have the kids “when I’m financially secure”.
I agree girls can do anything, but sometimes it comes at a cost. On an almost daily basis the women I meet are shocked to see how their fertility declines significantly with age. All too often their partners are also blissfully unaware how fertility declines. Below is a table showing the monthly chance of getting pregnant versus age:
| Women's Age |
Monthly Chance of Pregnancy |
Monthly Chance of Live Birth |
| 34 or younger |
26% |
22% |
| 35 - 37 |
22% |
14% |
| 38 - 39 |
17% |
10% |
| 40 - 41 |
12% |
7% |
| 42 or older |
8% |
4% |
In particular see how the chance of a baby drops dramatically in the mid 30’s. Why? It’s all about the eggs. Egg quantity and egg quality. The most eggs a woman ever has are before she is born. About half way through her own gestation she will have 7 Million eggs, but from there it’s all down hill. By birth she will have 1 Million eggs, by puberty 300,000, and by her mid 30’s maybe 25,000 left. Still sounds like a lot I know, but the other issue is that you tend to ovulate your best eggs when you are younger. The older women get, the greater the chance of a genetic problem in the egg. This largely explains the numbers in the table above.
Fertility treatments try to overcome this by increasing the chances of an egg and sperm getting together. This could start with some thing as simple as
Clomiphene (a tablet designed to help women release more eggs) through to
IVF where egg and sperm a brought together in the lab, and subsequent embryo quality can be examined, leading to selection of the strongest most viable embryo. The average chance of a baby from one cycle of IVF is now 45%.
It is estimated that within the next five to ten years there will be one child in every classroom born through IVF.
Girls can do anything….. except make more eggs. Career Planning needs to include Family Planning. We need to make work places more accepting of part time roles, breast feeding friendly, and if possible provide , more readily accessible childcare. Even with these changes it is a biological certainty that as women leave it later in life to have their children, a larger number of perfectly healthy women are going to need help because their eggs are fewer and of poorer quality. Women , and their partners need to take these factors into account when making choices about balancing careers, finances, and having children.