Introduction Pregnancy and the postpartum period is a difficult time for women living with HIV (WLWH) and postpartum engagement with HIV care is often reduced, with implications for health and well-being. We aimed to explore the postpartum health experiences of WLWH in relation to engagement in HIV care.Methods The NESTOR (iNvESTigating the pregnancy and pOst-paRtum health experience of women living with HIV) study was a UK based qualitative semi-structured interview study. 61 eligible women were identified. We used a purposive sampling technique to recruit women with differing levels of engagement in HIV care. Interviews were conducted via telephone or video call. Interviews were audio recorded and fully transcribed. We used a thematic approach for data analysis, and two researchers independently coded the data and established the key themes.Results 11 of 61 (18%) eligible women participated in the interviews, and the three main themes were 'infant feeding decisions', 'managing the risk of mother to child transmission', and 'managing the knowledge of their HIV status'. These themes offer detailed insights into the significant psychological and emotional challenges these women had experienced, and the practical support from healthcare professionals in both HIV and maternity services that had enabled them to navigate those challenges.Discussion There have been life-changing developments in the treatment and care for people living with HIV. However, even in the U = U (undetectable = untransmittable) era, traditional concerns about breastfeeding, risk of transmission to the infant and stigma continue to shape the postpartum experience of WLWH. As these impact on their emotional and psychological wellbeing, support in these areas needs to be prioritised. Studies report that postpartum retention in HIV care and viral load suppression are suboptimal for women living with HIV, where an important reason is the financial cost and access to healthcare. However, there is a relative scarcity of evidence describing the problems faced by women accessing HIV and maternity services within socialised healthcare systems, such as those in the UK.Women living with HIV face unanticipated challenges when becoming new mothers relating to disclosure of their HIV status, fears of vertical transmission and perceived perceptions of others deeming them inadequate mothers. Importantly, our analysis illustrates potential opportunities where intervention might mitigate the emotional and physical impact of these issues on their wellbeing throughout pregnancy and postpartum.