How accurate are dating scans?

[maryanngonzand]

I had a dating scan 2 weeks ago they said I was 8 weeks exactly which put my conception date around December 1st or 2nd. I then had another dating scan 2 days ago which put me 3 days ahead and said conception occurred around November 28th. I had sex on November 28th but I also did on November 12th and I'm wondering is there any chance I actually concieved on November 12th? Thanks I'm super worried about this and would appreciate any reassurance!

They're a guide.

It's impossible to say exactly when you conceived because sperm can live about 5 days and babies grow at different rates. That's why full term is 37-40 weeks

You’ll need a DNA test to know for sure, OP

They're supped to be accurate within a week. If there is more variance than that then it could be a indication that something is wrong.

It depends if your periods are regular and how early in the pregnancy (before 12 weeks). Conception is not determined by a scan. It's more of a guide for due date and gestational age of the baby. Some couples who have fertility treatment get a different date at the scan despite knowing the exact date of conception. If it's to decide paternity of the baby between two different men, the only way to know is a DNA test.

The 12th is pretty unlikely to be honest. What was the first day of your last period?

It's normal to have the date changed by a few days , I don't think it would be out by two weeks or more though

5-7days accurate.

Very unlikely to be 12th, there's quite a lot of difference between an 8 week embryo and a 10 week one.

They are accurate + or - 7 days. The two you've had were only 3 days apart in their estimates, which is a strong indication theyre correct. The most accurate time for a dating scan is around 12 weeks so the second scan is likely to have been slightly more accurate.

You very likely conceived on the 28th and it's extremely unlikely it was the 12th. However, if there are two men in the picture you are going to have issues either way and will probably need DNA.