# How Our Reproductive Potential is Determined Before Birth %%[[at 20 weeks gestation the fetus will hold the most eggs she will ever have]]%% At 20 weeks pregnant, my mother would not only be carrying me in her uterus but also half of her future grandsons. For this is the time when, in utero, in midfetushood, I would have all the eggs (follicles) I would ever need. And then some. Around 7 million eggs, in fact. The peak of my oogonial load.[^1] %%[[at birth a female will have lost millions of eggs already]]%% By the time I was born, I had already lost millions of eggs. Something that would happen through a process called apoptosis. This would leave me with around 1 to 4 million eggs.[^2] %%[[women start their reproductive years with 300,000-500,000 follicles]]%% This number would have dropped further by the time I approached my menarche. I would have around 400,000 when I had my first period.[^3] ![[egg numbers.excalidraw.svg]] %%[[a woman will have around 500 menstrual cycle's in her lifetime]]%% Despite this number appearing low compared to what I started with, it's not. Not when you think that we ovulate around 13 times per year. That equates to approximately 500 eggs in the 37 years from puberty to the end of our reproductive life.[^4] It's interesting, isn't it? How much of our reproductive potential is determined before we're even born. It's also a reminder of the incredible possibility for life that exists within each of us. Even before we take our first breath. [^1]: [[Woman by Natalie Angier]] [^2]: [[(Moghadam et al., 2022)]] Moghadam, A.R.E. et al. (2022) ‘Oocyte quality and aging’, JBRA Assisted Reproduction, 26(1), pp. 105–122. Available at: [https://doi.org/10.5935/1518-0557.20210026](https://doi.org/10.5935/1518-0557.20210026). [^3]: [[(Vigil et al., 2017)]] Vigil, P. _et al._ (2017) ‘Ovulation, a sign of health’, _The Linacre Quarterly_, 84(4), pp. 343–355. Available at: [https://doi.org/10.1080/00243639.2017.1394053](https://doi.org/10.1080/00243639.2017.1394053). [^4]: [[Human Reproductive Biology by Richard E. Jones & Kristin H. Lopez]] Jones, R.E. and Lopez, K.H. (2013) _Human Reproductive Biology_. Academic Press.