I have a 6 year old stepdaughter and I've been married to my husband for 3 years.

I'm now 20 weeks into my first pregnancy and I'm suddenly very worried about my son being around SD. 

Not because of her behavior but because she has HIV. Her BM also has it from being a caregiver as a teenager to an affected relative (documented). Supposedly there's only a 2% chance of transmitting it while pregnant, and SD was that 2%. DH is negative.