Does oestrogen level matter on letrozole?

Estella

Hey guys! I’m on cycle 2 letrozole 5mg. Had it day3-7. USS scan on day 10 shows 18mm follicle and lining that is on the thinner aspect (can’t remember exactly). Day 17 blood shows that I have ovulated with progesterone level 28nmol/L, which is great! But I notice that my oestrogen level is only 59, which is much lower compared to previous. Can anyone tell me why, and whether there is any consequences to that? Thanks!!!