Blood work during period

Rebecca • TTC #2 for 2yrs with pcos. Tried Clomid/metformin & injectables. First child born 14yrs ago. Failed IVM. Ivf worked!
So my ob/gun is sending me for blood work (Fsh-LH, Testosterone, prolactin) when/if I get my next period but didn't explain why? Can anyone please enlighten me?