My lmp was June,24th 2010 ,I have regular 28 day cycles. I am 13 weeks pregnant today actually , I have had three early ultrasounds and the dates given by the ultrasounds all match up exactly to my lmp on June 24th, here is my problem , on June 14h me and my boyfriend were on a break and I had sex with my ex I then got what I think was my period on June 24th. And me and my current boyfriend worked things out , so I guess you can say sex with the ex on the 14th was a one night stand. So me and my current boyfriend wanted to coneive, all my ultrasounds match up to my lmp of June 24th . So if I am 13 weeks pregnant now , by ultrasound and lmp does that mean I conceived 13 weeks ago? Or are they going by gestational age(lmp).. (which by gestational age calculators say I conceived between July 6-9th) ) is there ANY possible way the my ex is the father? Or is my boyfriend the father? How do ultrasounds measure.. by gestational age? Did I get pregnant after my period! Please help

Hi emmah765, welcome to AMHD... :)

Odds are great that the baby is your current boyfriend's. You would be farther along if your ex was the father, you had a period after the sex with your ex, and ultrasound puts the pregnancy later.

Ultrasounds measure the length of parts of the baby to determine gestational age. These are not exact, but are fairly close with early scans. Often there will be a slight adjustment since when using the last menstrual period most women are not actually pregnant for a week or two.

Gestational age is taken from the first day of your last period. Fertilizational age is from when you actually conceived.

Now, even though the odds are in favour of your current boyfriend being the father, it doesn't entirely rule out the ex. Was the last period you had normal for you? Same amount of flow, came when expected, lasted usual number of days? Your dates are close enough that it can't rule the ex out entirely... scans are not 100% accurate for dating a pregnancy... this is partly why you have a window of about 4 weeks at the end for what is considered a normal delivery time. If you want to know for sure, you would have to have DNA testing done after baby is born.

Thank you. If the other man was the father the ultrasound would measure gestational age about three weeks greater right? Because it would measure by the lmp BEFore the one on June 24th? So to ease my mind , you think the current boyfriend almost sure