Based on my last period I'm 7 weeks. At my ultrasound the baby was measuring 7 weeks too. I was expecting it to be under 7 because I conceived a week after my last period finished. I know because I used ovulation tests, had sex on the day I got a positive and that was the only time I had sex. Period finished 5th and I had a positive opk and had sex on the 12th. Is it normal for baby to be measuring ahead?