please help

[UnknownGirll]

Last period was April 18 (irregular periods) have sex with fiance everyday never got pregnant may 12 had sex with diff guy unintentioally later that night again with fiance. May 18 got positive result on home pg test. Due date according via u/s is Jan 24 2014 Please Help This Is Stressing Me Out AlOT

[AnnieBrooke]

Well, sure there is something to worry about.  You are engaged to one man and had sex with another man.  That is worth worrying about, in terms of what it means about how you feel about your fiance.  But as far as the dates are concerned, it sounds like you ovulated and conceived around May 3.

[UnknownGirll]

So There Shouldnt Be Anything To Worry About Right?

[AnnieBrooke]

The ultrasound looks at and measures the actual baby.  When you ovulated is extrapolated by the size of the baby.  If the baby is x centimeters long, it indicates a certain date for when the baby got started, at least in the early weeks.  So whether or not your periods are irregular, etc. is all swept away because they have the definite size of the embryo they can see before them right there on the screen.

[UnknownGirll]

Yes I Hope So i Just Got Thrown Off Because I Read Irregular Periods Make Yhu Ovulate Later But I Believe That Would Still Put My Due Date A Week Or Two Farther

[AnnieBrooke]

Sounds like you ovulated and conceived around May 3, then.  Not May 12.  Early ultrasounds are just not that far off.

[UnknownGirll]

Ultrasound Was At 5 Weeks

[AnnieBrooke]

It would be very unusual, but maybe not absolutely impossible, to get a positive on a home test only six days after conception.  It wouldn't even be easy to get a positive that early on a blood test.  

How early were you in the pregnancy when you got that due date, and was it from an ultrasound?  An ultrasound would be pretty reliable for computing conception up to at least tenth week, but if you got the due date by the doctor using a little wheel, or by ultrasound after your first trimester, it is not going to be as useful for pinpointing conception.

That said, the conception calculator gives the following, for a due date of January 24:

First day of last menstrual period:  April 19
Probable date of ovulation:  May 3
Possible dates of conception:  April 29 to May 7
Due date:  January 24 (40 weeks)

Especially because your positive was only 6 days after the sex with the other guy, the chances are most strong that the father is your fiance.  If you want to put the question entirely to rest, do a DNA test with the other guy after the baby is born.