Age and fertility
Like it or not, age is and remains the best predictor of fertility, in particular for healthy women.
The two main factors in fertility are the quantity and the quality of your eggs.
1. On quantity:
Menopause is when you’ve run out of eggs. Some women enter menopause earlier than others, but the average is about 51 (Morris et al, 2011). That number is pretty consistent regardless of your ethnicity (Eo et al, 2009).
Think of getting pregnant as needing to roll a 6 with a dice. Some people get it in one try, on average people need 6 tries, but some people keep rolling and rolling and are just unlucky. You should think of every month that you ovulate as one roll with the dice. This means that you have a limited amount of tries in your life. You stop ovulating about 10 years before you enter menopause, at about 41.
When you’re 30, you have 11 years x 12 months = 132 attempts of getting 6 left. By the time you’re 37, that number has gone down to 4 years x 12 months = 48 attempts.
If you knew you’d stop being fertile at 38 instead of 41, then suddenly you’ve only got 12 attempts left at 37.
Research shows that the percentage of pregnancies after 12 months of trying decreases with age (Hendershot et al., 1982). For different ages, this is:
20 to 24 years old: 86%
25 to 29 years old: 78%
30 to 34 years old: 63%
35 to 39 years old: 52%
Your chance of becoming pregnant also decreases per cycle. At age 30, this is about 20%, where for an age of 40 it is only 6% (Steiner et al., 2016).
Knowing when you’ll enter menopause is key in understanding your fertility. AMH is the most reliable predictor of ovarian reserve that we have, but it’s not perfect (Broer et al, 2014). Long story short: being younger is better, because it means that you’ve got more attempts left.
2. On quality:
It gets worse. As we get older, our cells get more exposed to bad things, and so fewer of the eggs that you release each month are viable.
Back to the maths:
For a 30 year old woman, about 75% of the eggs that you release are viable, and so think of the year that you’re 30 as 75% x 12 months = 9 attempts at rolling 6 per year. By the time you’re 40, that number has gone done to 5%. In that entire year, you’ve only got 5% * 12 months = 0.6 attempts of rolling 6.
Research underlines this, at the age of 30 years, 75% of women who become pregnant will also have a live birth. At the age of 35 this percentage has decreased to 66% and for an age of 40 this is 44% (Henri Leridon, 2004).
Imagine that your dice goes from 6 sides to over 20 sides, and you still need to roll 6.
The worst bit is that there is currently no way of knowing the quality of your eggs. We don’t have a test that can tell you what percentage of your eggs are good, or that helps you predict when you’ve released a very high quality egg. We’re hoping that through Grip we can eventually build a dataset of female fertility, and can help the research progress. You can help by allowing us to use an anonymous version of your data for science.