First Time Mom

Well I am a first time mom I am also 19 years old well I don't really know what to expect in pregnancy but anyways

I am 39 weeks & 2 days well in the beginning of my pregnancy my baby boy was so active always moved around all day and night but once I hit 38 weeks he was less active he still moved but only a little and the same thing is going on now that I'm 39 weeks he hardly moves but when I went to the doctor today and told them that they checked his heart beat and it was 160 which I am very proud that his heart beat is healthy and good but has anybody else dealt with this ? Is it normal for the baby to move less once you're closer to birth ?