Anyone know what this is?

So I am 23 weeks today and this showed up on my ankle. It is not painful or itchy. It's not raised, the skin feels normal to the touch.  My ankles haven't been swollen or anything. In fact I wouldn't even have known it was there except that my friend pointed it out and asked what happened to my foot. 
Has anyone else had anything like this? Is it something I should be concerned about?
I see my OB on Thursday so I will ask him about it then.. Unless I need to have it looked at sooner? What do you ladies think?