I've heard an early ultrasound is the most accurate way to predict conception date.
Ok, this is going to sound crazy, I have no idea how to fathom what to think... More than likely I know a paternity test may have to be done... I found out on Sept. 4, 2008 I was pregnant, Went to dr. on the Sept 16 and had a vaginal ultrasound... they told me I was pregnant with twins - overwhelmed, happy, then confused... they said
Baby A was 6weeks 6days EDD:5/5/09 & Baby B was 7weeks 1day EDD:5/4/09 Then ultrasound on Dec. 18 showed a girl 19weeks 4days and a boy 20weeks 4days. Last ultrasound was Feb. 27, 2009 saying the girl was 28weeks 5days and the boy was 28weeks 4days... They ended up having to come early due to a raise in my blood pressure. I had a C-section on March 20,2009 - My Daughter was pulled out first weighing 4lbs. 5oz. And my son came out second weighing 4lbs. 9oz. Both healthy needing no oxygen, and I pumped giving them breast milk for 2 months until I dried up...
My situation/problem is can you give me a narrowed down idea of my date of conception... There were 2 guys and during a certain time one was out of the picture for exactly 7 days... Please help ease my mind if possible... (altho I plan on pretty sure having to have a paternity test done.) Not to mention if my kids were not conceived on the same day, are they really twins, and is there a possibility that they each have a different father?
Please Help!
Lindsay

Strange but true: Twins can have different fathers | BabyCenter (http://www.babycenter.com/0_strange-but-true-twins-can-have-different-fathers_10364945.bc)

Superfecundation is the term for two ova impregnated at different times in the same cycle. Heteropaternal superfecundation if there are two fathers. The first word is often used for the longer term.

This doesn't mean that they have 2 fathers. Note how the ultrasound dates vary from one day apart to one week - and the boy and girl actually switched places in age for a while - not possible. Those are estimates only. Your fraternal twins really might be from the same father.

Also you can't 'predict conception.' Prediction is of the future only. Calculating conception is not possible. There are too many variables. Conception can happen within hours or can take as long as 3 days normally, as much as 5 days rarely, ultrasound is inexact, and length of pregnancy varies a LOT.

DNA is your only option, with FOUR possible results!
Both have father 1
Both have father 2
Girl has father 1, boy father 2
Girl has father 2, boy father 1.

I've heard an early ultrasound is the most accurate way to predict conception date.

That's like saying computer models are the most accurate way to predict the weather. How often is a meteorologist off the mark, even by a little? Calculating conception dates is an inexact science. ANY calculation can be up to 2 weeks off.

So the only way you will know for sure is with a DNA test. And you need to do it sooner than later. Because the likelihood of them finding out is pretty good.