Women who acquire HIV during the pregnancy and breastfeeding periods have a higher risk of transmitting the virus to their child than women who become infected with HIV before pregnancy. We explore the context of sexual beliefs and practices that may shape both HIV risk and willingness to use HIV prevention products during pregnancy and postpartum in Malawi, South Africa, Uganda and Zimbabwe. Twenty-three single sex focus group discussions and 36 in-depth interviews took place between May and November 2018 with recently pregnant or breastfeeding women, men, mothers and mothers-in-law of pregnant or breastfeeding women, and key informants. Participants across study groups and sites (N = 232) reported various perceived benefits and harms of sex during pregnancy and postpartum. Participants discussed reasons why men might seek sex outside of the relationship. There is a critical need for alternative prevention options to protect pregnant and breastfeeding women from HIV.