Gestational Age

How many mommies' babies were older than they originally thought? My periods were never regular so I'm not really sure when the last one was. I went to the doctor to get an excuse for work and turned out I was pregnant! I gave them the date of January 13th as LMP but now that I'm "22 weeks" my ultrasounds are measuring big and his gestational milestones such as moving, hearing, detecting heartbeat via doppler etc seemed to have come earlier than expected. Anyone else experienced this and their baby come sooner? Even just by a couple weeks?