How accurate are ultrasounds at dating?

I have received 3 ultrasounds during this pregnancy and going to have my 4th on Thursday.
Why so many? I had my first at 9 weeks for dating purposes, my second routine one at 20 weeks, one at 24 weeks to look at his spine and kidneys and this one coming up at 36 weeks for fetal weight. All of my ultrasounds have given the EDD of 8.20 which is exactly what my due date is from LMP, is it strange for it to be that exact? I ask because everything I read on here makes it seem as if dating is incorrect more times than not.

This just means that you ovulated exactly on cycle day 14 or close to that. Your baby is growing at the proper rate and it's not uncommon for it to be perfect. I work at a fertility clinic and we monitor early pregnancies, up to 10 weeks. Sometimes the dating is off by a day or two, but since we know the exact date of ovulation, we are able to go by that and usually it is dead on unless the fetus is growing slower or the embryo implanted later than expected. We have people come in being pregnant for 6 weeks and 5 days and their measurements are the same, 6 weeks and 5 days.

Ultrasounds a very accurate.

Actually they do so many ultrasounds cause not everyones babies grow at the same rate. Sometimes they can be off but usually are really accurate because they are going by the babies size.

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