I went in for my 5 month ultrasound at 19 weeks only to have to be rescheduled in two weeks because the doctor said the baby only measures 17.5 weeks. Is that normal? The heartbeat was 156 beats per minute, and there was plenty of amniotic fluid surrounding the baby. And they tried to find the sex anyway but he said it was too early to tell. Well there was nothing there meaning no boy parts sticking out. Anyway my question is, do babies sometimes NOT match their gestational age?