Drug resistance is uncommon in pregnant women with low viral loads taking zidovudine monotherapy to prevent perinatal HIV transmission.

Zidovudine monotherapy is used to reduce perinatal HIV transmission in women with low viral loads. There are few data on the risk of drug resistance in this select cohort of women. We determined the prevalence of newly acquired mutations conferring reduced sensitivity to zidovudine after exposure during pregnancy, and found that the development of mutations was uncommon and was restricted to women treated before 1998 who had higher baseline viral loads than those currently recommended monotherapy.