Welcome to our Forum. You questions raise several important issues. I'll be happy to comment.
First things first. There is a widespread misperception that exposure to blood, and particularly menstrual blood, changes during sexual the risk for infection. That is not the case. While several STIs are also transmitted in blood (HIV and hepatitis B in particular) in general, the amount of infectious microorganisms in blood is no higher and sometimes lower than the amount of organisms found in genital secretions. Further, just as is the case with genital secretions, surface contact with skin does not lead to infection. For these reasons, the blood exposure you describe does not change the risk for infection.
Secondly however, if your partner was not beginning her period, vaginal bleed during or immediately after intercourse is sometimes a sign of the presence of an STD such as chlamydia and may be a good reason to get checked for STIs. that your partner is seeking evaluation is a good idea.
As for your risk, as implied above, your exposure was condom protected and that means that there is no meaningful risk for infection from the exposure you describe, nor any reason for testing.
I hope these comments are helpful. EWH
correct, this is not unusual. You need to not worry. EWH
Thank you for your informative reply.
To follow up, I spoke to the girl again today and indeed it looks like it was her period. She was surprised as she is usually very regular and didn't expect it to come so early (it was a week early), but it appears her period is what it was.
Am I correct in assuming that a early or late period in a woman who is normally very regualr is not that unusual? Thanks again.