Hello, I'm currently 35 weeks pregnant exactly according to my cycle. …

Hello, I'm currently 35 weeks pregnant exactly according to my cycle. I had an ultrasound today, the baby is 30.5 weeks old, and I don't understand how this can be, because I had an ultrasound on July 16th at a private clinic with a good doctor. I wasn't told about any delays, and the ultrasound showed almost 30 weeks already. Is it possible that the baby didn't grow in a month?