Is an ultrasound EDD accurate if your period does not last normally seven days?

the EDD is the estimated date of delivery, with both of my children the edd was not correct. my first was born a week after the edd which was the date of conception plus 40 weeks. my second was born 10 days prior to the edd but i also had 4 different edd.

Estimated Date of Delivery is just that, Estimated. A baby can be born from 3 weeks before up to 2 weeks after with no problems.

With my first, his scan EDD was 10 days later than my period EDD and he was born on the scan EDD.

Second time around (twins) the scan and period EDD were the same but I was induced 4 weeks before with pre-eclampsia.

The only EDD that is accurate from an ultrasound is one done in the first trimester. The earlier the ultrasound is performed, the better. We measure what is known as the crown-rump length (the measurement from the top of the head to the baby's backside), and this measurement is the most accurate in predicting an EDD. First trimester ultrasounds are typically accurate within a week of how far along a baby actually is. Second trimester ultrasounds are up to two weeks off; and third trimester ones are up to three weeks off. What we are measuring, though, is how far along the baby really is--not when the baby will be born. As someone else mentioned, a due date is only an estimate--and only 5% of women actually deliver on their due date.

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Dr. B.