I have an anterior placenta and am pregnant with my second. I felt my first clearly at 16 weeks. I started feeling my second at 16 weeks too, but very lightly. In fact, it was so light that I could only feel it lying flat on my back and holding my breath. I started feeling him better at 20 weeks. I still only feel him late at night when I'm flat on my back, but I don't have to hold my breath. I'm 20+5 now.