That's about the size of it

Keeping tabs on your girth growth does more than clue you in to how much your wee one is changing inside you. The size of a mom-to-be’s bump can also predict troubles beneath the surface, such as slow fetal growth (aka intrauterine growth restriction). So, pull out the measuring tape to make sure you’re expanding on track. Your health care provider will do the same starting around 20 weeks.
How to measure
Instead of calculating your circumference, your doctor or midwife will measure the height of the fundus—the distance from the pubic bone to the top of the uterus.
Find your number
Once you’ve passed the 16-week mark, your fundal height (in centimeters) should match your number of weeks’ gestation. So, if you’re 22 weeks, then you can expect your fundal height to be around 22 centimeters. If you’re measuring larger or smaller than the norm, it doesn’t mean something is wrong. (It could just be you have a full bladder!) And a smaller bump doesn’t guarantee a smaller baby. How you carry depends on your height, weight, muscle tone and whether you’ve been pregnant before (among other factors). Every woman’s body progresses at its own pace, but chat with doc if you’re concerned.