How accurate is an Ultrasound!
I had my last period on March 20th.
I had sex on the 27th, 28th, 29th,30th. Then again on April 4th, 5th, 6th, 7th and 9th.
I had my ultrasound recently and she said I was 17 weeks and 2 days. (This was a few days ago) I counted back 17 weeks and 2 days. And It was the 26th! How is that possible if I didn't have sex until the 27th and then on? The 26th was 7 days after the start of my period. My period was just finishing up then

Early ultrasounds are very accurate.

If your period started March 20, then as of today, July 28, you are currently 18 weeks and 2 days with a possible conception on or around April 3 or 4.

How is that correct. The ultrasound woman is saying right now I am 17 weeks and 5 days as of today. If you count back 17 weeks and 5 days. It's the 26th of march. I did not have sex on that day or previous days. I started my period March 20th and never had sex until the 27th.

Because they go by average size, it is never exact to a specific day, it is give or take a week at the very best. So count back 16 week 5 day and see what that gets. Then all days between.

There is never one exact date if that is what you are thinking

If you count back 17 Weeks from today. Then you get the day that I supposably ovulated. I understand that I just didn't understand how she got I was 17 Weeks and two days pregnant.. (on July 25th)