How can you determine who got a girl pregnant?

NIPP. Non invasive paternity testing can take a sample of the mother's blood as early as 8 weeks into a pregnancy. Fetal cells that circulate in her blood are separated out & tested.When compared to the designated father it can confirm paternity.There are other methods that can be done later in pregnancy or after the kid is born.DNA study is the standard.Guessing based on timing is a waste of time.