14 or 15 weeks?

[Mama2b91]

I'm a bit unsure as to whether I am 14 or 15 weeks pregnant. I thought my due date was the 21st of December. But at my 12 week ultrasound the midwife told me the baby looked a little bigger and said I looked 13 weeks so she changed the due date to 17th December. For some reason this doesn't feel right because the first date of my last period was the 15th of March which would mean I ovulated around the 29th? So my due date should be the 21st?
I'm just a bit confused x

[jkgeary]

due date isn't a deadline. its a guess. always think 2wks before or past could be the big day.

[Masoak]

They did the same to me my due date was the 14th according to my last period but hanged it to the 7th because I was showing a week more..i asked the Dr why that was because of my last period and she said sometimes u ovulate differently..I'll take the earlier due date!

[AnnieBrooke]

Did you have any earlier ultrasounds than 12 weeks?  Most doctors will say that by the twelfth week, the accuracy of an ultrasound for determining when conception occurred is suspect has a margin for error of plus or minus 7 days.