Why are doctors off a week are so during pregnancy if someone had sex at the end of December and the due they got counting backwards says they conceived jan 13 is there possibly of another partner being the father

THey are off more than a week, it's a guess of Plus or minue TWO weeks. THat means its an entire month that's possible.

Its because Medical science can't be any more precise than that...

But DNA testing can resolve the issues for people that like to sleep around.

Dating is Best Guess and not definite.

THey are off more than a week, its a guess of Plus or minue TWO weeks. THat means its an entire month thats possible.
So most likely if that's es tr last time she had sex that's the father wellhead could just be saying that but does it add up to you
Its because Medical science can't be any more precise than that.....

But DNA testing can resolve the issues for people that like to sleep around.

Ok but does it make since if that's the last time she had sex well so she says are should I expect to take a DNA test to make sure I mean if it adds up I won't bother

So you are having sex with your sister?! https://www.askmehelpdesk.com/pregnancy-new-motherhood/does-add-up-702275.html Specifically post #16.

Doctors aren't "off."

You see we don't have a camera inside of the fallopian tube to know when the sperm meets the egg. We only have the information regarding the LMP (Last Monthly Period) that the woman, in your case your sister, gives us and we have to trust that she is telling the truth.

Pregnancy can go two weeks either way as Smoothy said above.

Ok but does it make since if that's the last time she had sex well so she says are should I expect to take a DNA test to make sure I mean if it adds up I won't bother

Wow dude. Why would you have to have a DNA test for your sisters baby? That's messed up.