How accurate are due dates via ultrasound?
Ultrasounds are pretty accurate early on at determining when you’re due. They measure body parts of the baby and, early on, most babies are around the same size. Once you get further along, babies tend to grow at different rates, but in your first and second trimester, they’re about the same. So I would go by the ultrasound unless you know pretty close when your last period was (within a few days). Our ultrasound was almost exact. We knew date of last period and date of conception and the ultrasound average was only 2 days off what our actual due date was.