Measuring Weird

Kam

In the beginning when they started measuring my stomach with the measuring tape I was right where I was supposed to be always the same cm as I was weeks along. But recently I've been measuring weeks behind or a week behind, in my ultrasounds the baby is measuring right on time. Just wondering if this happened to anyone else, and if it'll affect when I go into labour? 37 weeks today, measuring 36 cm, last week was measuring 32 cm.