Yep, for the most part you'll measure as many cm's as you are weeks. So 23 cm at 23w is right on the dot. But it's not unusual to measure a couple cm's either way. I was right on every time with my first two, but about 2 over everytime with my last. I had a lot of amniotic fluid, which is why I measured big. And of course mulitiples will measure bigger.