Understanding Fundal Height in Early Pregnancy: What to Expect

Question
My daughter is 18 and pregnant for the first time.  She started showing in the first month and was wearing maternity clothes at 5 weeks.  She is not overweight and has actually lost 5 lbs since becoming pregnant.  She had two early US that confirmed the dates.  At her last OB appt last week at 14 weeks, her midwife said her fundal height was about a 16-17 week pregnancy.  Five days later it was already up to her belly button.  I know that would usually be where a 20 week uterus would be.  What could be the cause of her uterus being so large?  She thinks she has already been feeling movement in the past week also.  Isn't 14 weeks very early with a first pregnancy?

Answer
There are many reasons for a high measurment.  Twins or more could be a cause. (with U/S you know this is not the case with your Daughter)
Lots of fluid, a large baby, or a larger than "normal" uterus.
I did the same thing with my baby, I ended up having a pretty good sized baby as well as having a large uterus.
Babies move almost all the time from conception. It is only when they get bigger the mom can feel it.  Some women (exspecially if the baby is big or the mom is small) feel the movement sooner than others.
Good luck.