norms

Is the word norm what I should say

I'm not sure whether to say 'in the norms' meaning it is the right size. Would you say 'for its age' when talking about a fetus?
How would you say the following?
Your fetus is in the norms for its age. It is 10 cm at 15 weeks.

Here is the chart I'm talking about
http://www.babyyourbaby.org/pregnancy/during-pregnancy/fetal-chart.php

Thanks