Soo confused about birth date

[Pregnantbrittany]

I went to the doctors with the thought that I was due on March 13th (health Department) when I went to the doctors he listened to the heart beat and measured my tummy and told me I was a lot further along than I was originally told and scheduled an ultra sound but when i went to the ultra sound they said I was due march 27 th I am having trouble determining the father and this is a big difference I need to know if the baby is my ex or current bf I don't understand how the doctor thinks I'm further but the ultra sound says I am less pregnant I went from 19 and a half weeks and allegedly further to  16 and a half weeks

[DADAT47]

Go by the ultrasound and whatever gestational age they give the baby at that scan go back that much on the calendar from the date of the scan then go forward 2 weeks and that would be approximate date of conception.

[Smileymarie]

Not Really , I Had Sex Close To My Period && I Had Absolutely No Spotting Except For When The Egg Was Implanting && That Wasn't Even Noticeable .

[Pregnantbrittany]

The ultra sound gave the exact date I was with my ex wich is what I am scared of. We had sex on 4th of July and I didn't have my period but I start my period on the 10-12th would I have had some spotting or a light period if I got pregnant that close to it

[Pregnantbrittany]

But how does that explain my actual ob thinking I am further because of the heart beat and tummy size (by the way I am small I never gain weight with my baby's other Than Tummy and breasts (this is my second)) and him being completely wrong according to my ultra sound

[Smileymarie]

It's Ok , I Had The Same Problem . Me && My Child's Father Broke Up For A Couple Of Months && When We Got Back Together I Found Out I Was Pregnant After A Couple Of Weeks .. Don't Freak Out The Doctors Add A Couple Of Weeks To Your Pregnancy Because They Can't Determine The EXACT Time That You've Conceived . But Honestly The Only Way You Could Really Find Out Who The Father Is , Is If You Do A DNA Test .

[Sam_v]

The ultrasound is probably a k 're reliable source. I went to the doctor at about 7 weeks and then went back 9 weeks later and the doctor said by the size of my uterus I was at 9 weeks which I knew wasn't possible the ultra sound I had done later that day showed I was 16 weeks

[San408]

You could of ovulated later or earlier than expected, the only way to be for sure on who the father is. Is to have a dna test done when baby is born.