Measuring WAY off.

Brianne
So, I went in today for my monthly appointment. My OB had to measure my fundus 3 times because I'm measuring 29 weeks and I'm only 23+1. They want me to come back in 2 weeks to get measured again and if I'm still off, they want to send me for another sono even though I just had one 2 weeks ago. Eesh. The first thing the doctor did was check to see if I'm having twins and every sono has come back singleton. Does anyone know what would cause measurements to be that different?