About ultra sound test

Hi, i made an ultra sound test and the doctor told me that the size of the baby is 3 mm. can you tell me how many weeks old is it for this size? is it 5 weeks old or less ?

Fetus of 3 mm CRL (size) is about 5 weeks old

Hi When is the first time that i can do ganetik chacks? ?to Know who is the father Is it on the on the shafir water test on the 3th month or that i can do it before?