If you know you're HIV positive but are otherwise healthy, your pregnancy should not be affected, and there is no evidence to suggest that pregnancy increases the risk of developing full-blown AIDS. Any infections should be treated at once, and by taking iron and folic acid you can reduce the chance of becoming anaemic. You should also make sure that you've had a cervical smear and appropriate treatment if necessary.
If you received no treatment, had a normal delivery, and breastfed your baby, the risk of passing on the infection would be about 20 per cent. By reducing the amount of virus in your bloodstream while you are pregnant, having a Caesarean delivery, and not breastfeeding, the risk is certainly less than five per cent and possibly as low as one per cent. New effective drug combinations (the most common is known as "triple therapy") reduce the amount of virus in the body and seem to be safe in pregnancy.
Most large hospitals have special arrangements for HIV positive pregnant women. Your care is likely be shared between an obstetrician , specialist midwives, and an HIV/genito-urinary physician. Tests in the first few months are nor accurate, as the baby will probably have HIV antibodies in its blood that have come from you and crossed the placenta. An antibody rest can be done after a year.