Anyone that can help?

Your calculations seem right as far as you being close to 20+ weeks but keep in mind that when you have the ultrasound it is the measurement of the fetus so it can vary depending on the ultrasound technician that is doing the measurement, but usually it isn't that far off. Also the fetus could be angled in a way that may not allow accurate measurement.

Now with the two possible fathers, you ovulate about 14 days, more or less, from your last menstrual period...seems like the guy that you slept with on the 27th is more likely to be the one who got you pregnant(sperm can live inside the uterus up to 6 days). You had sex on the 12th day from your last menstrual period so this person is closer to the time you may have ovulating... this doesn't count out the other guy thou because they are about a week apart. Hard to tell get a DNA test to be sure.

If dated from your LMP, which was the 15th of March, you are about 21 weeks pregnant right now. The 31st was two weeks ago, which wuld have put you at 19 weeks pregnant. They may have been stating your date at the time, 16 weeks, based on the actual fetal age which is always 2 weeks less than the date based on your LMP. If this was the case, that would put you at 17 weeks. Only one week less than that would put you at 16 weeks, and that one week could be easily explained by normal variations in fetus size. In fact, a baby can measure up to two weeks ahead or behind and be normal and your due date stay the same. Even if the baby does measure farther off than that, it doesn't mean anything is wrong. And they would just change your due date.

At your scan when you get the date, ask for clarification as to where they are dating from.

ok, a woman ovulates on the 14th,15th, & 16th day, sometimes the 17th day, after the first day of her period. so, you were ovulating around april 5-6, so that guy is most definitely the father. i know that's not your question, but i just thought you should know that. that was about 18 1/2 weeks ago, so the ultrasound must have been pretty accurate. actually, it was accurate. the baby could be under weight for a number of reasons like undereating, drinking, or drug usage.

i hope this helped you, but you really need to start practicing safe sex.

Unfortunately an ultrasound won't tell you who the father is... sorry.. It's going to get even harder to see how big the baby is as it grows so scans/measurements can be off... but it's not going to pinpoint who the father is because what of the week, well little over a week between the guys? Did you know sperm can live up to what 5 days inside of you waiting on your egg to be released..sorry you're going to have to tell both they could be the daddy and get DNA tests when the baby is born...

So I did the whole due date calcualtor with the information that you gave me and you are now 20 weeks pregnant. Which means you were probably 18 weeks when you got the ultrasound. 16 weeks is 2 weeks off from the normal due date.. hmmm. Did you talk to your doctor about it. It seems confusing to me as well because it's not off by a whole period.

The dates can change a lot, and their too close together to tell you who the father is. You need to tell both of them and have a DNA test.

Wow... confusing. I would say the ultrasound is pretty accurate.