HIV positive pregnant women are vulnerable to AIDS defining illnesses in much the same way that non-pregnant HIV positive women are. The medical management HIV related complications in pregnancy is complicated by the requirement to balance the needs of the mother and the foetus, and the viability of the pregnancy itself. The health and survival of the mother are paramount. There is unlikely to be foetal survival without maternal survival. This can give rise to complex medical, practical and ethical dilemmas and these cases need to be managed with close collaboration between HIV specialists, obstetricians, paediatricians and, where possible, specialists in obstetric medicine and materno-foetal medicine. Radiologists, intensive care physicians and other specialist medical and surgical teams may also need to be involved.

Physiological changes in pregnancy are important to understand as they can impact on the interpretation of test results, clinical findings on examination and the pharmacokinetics of both HIV and opportunstic infection drugs used in pregnant women. CD4 cell counts characteristically drop during pregnancy. Furthermore there is a shift from cell-mediated immunity (Th1 response) toward humoral immunity (Th2 response) which leads to an increased susceptibility to, and severity of, certain infectious diseases in pregnant women, irrespective of HIV infection, including toxoplasmosis, varicella and listeriosis. There is an increase in cardiac output (30–50%), plasma volume (24–50%), red cell mass (20–30%) and glomerular filtration rate. Absorption of aerosolised medication may be affected by an increase in tidal volume and pulmonary volume. Placental transfer of drugs, increased renal clearance, altered gastrointestinal absorption and metabolism by the foetus may affect drug levels. Therapeutic drug monitoring (TDM) should always be considered due to altered drug pharmacokinetics in pregnancy, and the potential for complicated multiple interactions between antiretrovirals and many of the drugs used to treat opportunistic infections