Newbie with a question!

I'm completely new to this site. But my husband and I were lucky enough to have 3 girls and we decided to try for 1 more. He is getting a vasectomy in December. So my time is limited. I used my calendar as my profile pic because I didn't realize until this moment I could post it here. (Oops) 

Anyway, I went to my OB for something unrelated and it turns out I'll need imaging done. I told her how we are trying and she recommended I come back on the 18th ( next Wednesday ) for a blood test. 

Would it show anything that early, if I was pregnant??

Thanks so much for your help