Which hormone is the best indicator of fertility?

Question

I want to perform a simple blood test on a group of women to gauge their fertility (relative to one another).

I was thinking estradiol, but then women taking birth control would mess up the study because most birth controls have synthetic estrogens.

So what is an easy way for me to compare fertility between different women?

Answer 1

luteinizing hormone (LH)

Answer 2

Higher progesterone levels in second week of menstrual cycle suggest higher fertility.