Function gives you access to lab tests that measure the primary fertility hormones in women and men. These are critical for those trying to conceive. See the list here. You will need to work with your doctor to discuss your fertility based on your results.
Note, if you are on hormonal birth control, some fertility markers are not tested, given birth control's propensity to greatly skew results.
If you have a regular period, you will have to get tested on day 3 of your cycle for the most optimal result.
Beyond the obvious tests directly related to fertility, other tests that are part of your Function membership can impact decisions around conceiving, including heavy metal toxicities.