Conception based on ultrasound

[Tayrei1521]

I have very irregular periods so As of 11-19-15 the baby is measuring 18weeks, 2 days. Online it says subtract 2 weeks from that and you have your "conception date." I did that and the conception date says 7-14-15. So did I conceive around that day? I'm only asking because I was with a long term boyfriend and we broke up 7-20-15 and I made a oopsy and got drunk and slept with someone else 7-28-15. Now me and long term boyfriend are back together and I want to be sure it's his and not the one night stand that happened.

[AnnieBrooke]

Well, please talk the whole question over with your doctor, so you understand what he means when he says your ovulation was probably weird.  You've got an extra two weeks in there to account for, and April 19 does point back to right around the time you had an oopsie, so you need to understand why he is saying April 19 but then saying your ovulation was weird.

[Tayrei1521]

My due date is April 19th, the dr said my ovulation was probably weird. My 8 week ultrasound the baby was measuring big but he didn't change my due date

[AnnieBrooke]

Were you given the same due date at your 6th and 8th week ultrasounds as you have now? (What is the due date, around April 5?)  

[AnnieBrooke]

It sounds most like your boyfriend's baby, but please keep in mind that as your pregnancy progresses, using an ultrasound to assess your conception date becomes less accurate (or can be less accurate).  Did you have an early ultrasound, or was your only one the one on November 19?  

[Tayrei1521]

I had a 6 week ultrasound. And it was the same. And also had an 8 week and 12. And I know for a fact I didn't have my period the week of the 7-14-15 I probably had it the last week of June. And boyfriend and I have been very sexually active with no use of protection.

[Tayrei1521]

Commenting on the post above, my sister is a week behind me and she got pregnant on her honey moon week of 7-18-15----7-24-15 so I got pregnant the week before right?