Hello
Thanks for writing to DoctorSpring.com with your health concern.
Frankly, December 4 and December 6 are really close by, just 2 days apart.
Even a first trimester ultrasound scan , which is most accurate for dating a pregnancy, has an inherent error margin of upto 5 - 7 days.
So you cannot rely even on that for determining the father.
Frankly, a DNA paternity test is the best option for you.
Before that, one thing can be done, you could request the man with the vasectomy to get a semen analysis done.
IF there are live sperms in his ejaculate, chances are really good that he could be the father.
Vasectomy does not fail that commonly, so again that is an issue in itself.
However, condoms when used correctly too fail rarely, so why not get a semen test done, to determine whether or not you go on to the paternity test.
All the best
Please feel free to discuss further.
Patient replied :
He did have a semen analysis done in August and it came back no live sperm.
Hello
Thank you for your follow up query at DoctorSpring.com
Even though there were no live sperm then, its possible vasectomy failure may have occured between August and December. That's why a retest is presently required.
The only way to determine the paternity of the pregnancy with 100% accuracy still remains to do a paternity test.
Hope this helps, feel free to discuss further