Hello Thanks for writing to us with your health concern. It is just not possible to determine who is the father without a paternity test. This is because the two encounters are two closely placed. they are just 2 days apart in fact, even early trimester scans have an inherent error margin of upto 5 - 7 days. So clinically speaking, you NEED to have a paternity test to establish who is the father. Blood samples taken from the mother, baby and the man thought to be the baby s biological father can then be tested for DNA fingerprinting and in a large proportion of cases can prove whether the man in question is definitely the father. It is technically possible for a blood sample to be taken from a baby whilst it is still in the womb. This can be done by amniocentesis or CVS . However, lately, paternity testing can be done by collecting mother s blood sample too, anytime after 8 weeks, and is upto 99 % reliable. Please consult your obstetrician and go for Paternity testing as it is a vital question for your life. All the best Please feel free to discuss further by writing in at - http://doctor.healthcaremagic.com/doctors/dr-aarti-abraham/64623 Take care.