Why is my scan dating at 7 weeks.

[Maddiee71]

I had unprotected sex once 5 weeks ago. I went for a scan 2 weeks ago and they said they said they saw something measuring at 2.5mm but couldn't be sure if it was blood, fluid or the pregnancy and gave me a leaflet on unknown locations in pregnancy and told me to come back in 2 weeks for another scan. I went back yesterday for another scan and they said the fetus in now measuring at 8.5mm and they dated me at 6 weeks and 6 days. How is this possible?! I can't make sense of any of it can someone help

Pregnancies are normally dated from the last day of your period not when you had sex. So if it was 5 weeks ago that would make you about 7 weeks pregnant. That remains the case even after a dating scan!

A pregnancy is dated from the first day of your last period. So you are 2 weeks pregnant by the time you get pregnant.

Because they start the count from the first day of your last menstrual period?

I had a coil in for 5 years and had it taken out in June and one small bleed in August and nothing after that.

So they work out how far along you are by measuring the baby, but obviously your measurements will be put into a calculator along with all the women who do know when their last period would have been, which still makes your baby measure around 7 weeks?