Anyone have this happen?

So I'm 38 weeks with my first baby and just had my weekly apt. Last week and this week my fundal height was measuring at 36 weeks...my babies heart rate is great 150 and her movements r normal and consistent but my doctor ordered an ultrasound just to get a more accurate reading of the size of baby and to make sure I am producing enough amniotic fluid in there. She said there is no need to worry but I am a huge worrier when anything out of the ordinary or any concern arises!...just curious if this has happened to anyone else?? If so what was the outcome?