Due Date doesn't match LMP

[bundleofJOY0424]

I am currently pregnant in my third trimester. Initially I didn't know that I was pregnant for about 5 months and was studying in Beijing at the time. When I finally got home to see a doctor they told me that I was 28 weeks pregnant with a due date on Oct. 7th. To me this ddidnt make much sense because it doesn't match my LMP which was most likely (unfortunately I can't be 100% on what the date was) of December maybe (very slight chance) that it was in the second week of December. The main issue is that I'm not sure who the father is. In the month of December, the possible dates that could be the date I convieved are either Dec 19th or Dec 25. I've never praticularly kept track of my cycle so I'm not sure if its irregular and that's the reason for such a wide gap between the ultrasound and my last menstral period but I am quite worried. I didn't plan for this pregnancy but now that I am pregnant I am estatic and ready to be a mother. Some clearity on the situation would definitely make my nights shorter. This stress isn't good for my baby at all.

[AnnieBrooke]

A due date of October 7th, according to the conception calculator, gives you the following:

     Probable date of ovulation:  January 14
     Possible dates of conception:  January 10 to January 18

However, if your ultrasound was not until the 20th week, it could be a bit off.  I have heard estimates of a week off at 12 weeks (though that seems excessive) and by that logic, you have to allow for the possibility of more than a week by 20 weeks.  But I read an article in the journal Perinatology that says ultrasounds up to 20 weeks are accurate plus or minus only a week.  So in other words, I would not use a 20th-week ultrasound to include the guy on the 18th --  that is too far off January 14.  But it could possibly be the guy on the 25th (not the strongest chance) and it could certainly be anyone from January 10 - 18.

If these guys were just people you met while there, I don't know what to tell you about how to get in contact with them.  If it was through a group or academic program, it would be easier.

If I had a choice of the guys to contact in order, it would be Mr. January followed by Mr. Christmas, and I would not be too concerned about Mr. 18th of December.  Sorry I can't help you more.

[bundleofJOY0424]

I did have sex in the month of January but all those possibilites are all similar. As in either way the baby would be black. But if it is between the guy on the 18th (caucasian) and the guy on the 25th (black) then I would be able to figure it out by race.
So for sure I should be looking at the month of January then? Even though I didn't have my period that month?
Have no clue how I will get in contact from accross the world.

[AnnieBrooke]

Another question -- will you be able to tell by looking, when the baby is born?  In other words, did the possible dads all look alike or very different (such as, one was Chinese and one was Caucasian)?  I'm trying to figure out how stuck you are if you need to get DNA tests done from across the world.

[AnnieBrooke]

Did you say you had sex in January but don't think that is the father because you didn't have a period in January?  Or did you have no sex at all in January?

[bundleofJOY0424]

When I was still in China I had two u/s. The first on May 24th saying that I was 20+ weeks and the second on May 28th but that one said that I was 22+ weeks. Which would make the due date for the first Oct.11th And Oct. 1st ... Its just all very confusing. So at this point there is no way to be sure when I concieved?

[bundleofJOY0424]

Is it possible for to have been ovulating and have conceived at a time when I didn't have my period at all? I am sure that during the month of january that I didn't have a period at all.

[AnnieBrooke]

Unfortunately, having an ultrasound as late as your fifth month means that you have to say "plus or minus two weeks or more" on all dates it provides, because some babies grow faster than average and some grow slower than average.  If you are trying to split the difference between two guys who are six days apart and the tolerances on your measuring method have that large a margin for error, there is simply no way to do it.  

But are you sure your problem is December 19 vs. 25?  Unless the ultrasound was really far off, it sounds like you conceived in the middle of January.  A due date of October 7th, according to the conception calculator, gives you the following:

Probable date of ovulation:  January 14
Possible dates of conception:  January 10 to January 18

Even if your ultrasound was off because the baby grew faster or slower than average, it's still pretty far from conceiving in December.  Did you have sex with anyone at all in January?