Denied Promotion due to Pregnancy

I have been employed with my company for over a year and a half. I was promoted to asst. mgr. after my probationary period and was told that when the mgr. position was available it would be mine. I continued to rank #1 in our company for most sales and was consistently the top producer at my location. Every few months the mgr. would brag to everyone about how good I was and I even took the place of the Sales Mgr. for 3 months while she was out. I knew they weren't too keen on having pregnant employees in new positions b/c a former employee was terminated within her probationary period after it came to light she was pregnant. This was discussed in several of our meetings but was covered up by her so-called "poor" performance.I informed my employer last month that I was pregnant. Shortly after, the position of Sales Mgr. became available and I was told last week that he was positive I would get it but he had to go through the formalities of allowing others to interview for it so it would not seem as if it was "given" to me. Today he told me he decided to go with someone else. Would this be a form of discrimination because he has told me and several others that this job was mine and now that I'm pregnant its not?