Is there a chance I could get pregnant after my husband's vasectomy?

I have been spotting dark blood for about 6 days. I did a search and there was a few articles on how it could be related to early pregnancy. My husband had a vasectomy last fall. He never went in for clearance and told me it was fine. I would not mind another baby. I would just have my hands full because both of my children are in school now . Could some one please tell me if they know any thing about it. Thanks.