There is no proven benefit for the routine use of therapeutic drug monitoring in HIV-positive pregnant women either for improving viral control or preventing mother-to-child transmission. This analysis reviewed a cohort of 171 HIV-positive pregnant women delivering between 1 January 2008 and 28 May 2013 to first establish which baseline characteristics are associated with having therapeutic drug monitoring performed, and whether therapeutic drug monitoring was associated with improved HIV control during pregnancy or mother-to-child transmission. Therapeutic drug monitoring was performed in 39% (n = 66) of patients; it was associated with baseline characteristics of poor adherence to therapy (therapeutic drug monitoring 23% versus non-therapeutic drug monitoring 10%, p = 0.025) and the use of protease inhibitors (therapeutic drug monitoring 94% versus non-therapeutic drug monitoring 77%, p = 0.005). By multivariate analysis therapeutic drug monitoring was associated with medication alterations during pregnancy (therapeutic drug monitoring 68% versus non-therapeutic drug monitoring 12%, p = < 0.001), but not associated with any difference in viral load breakthrough during pregnancy (therapeutic drug monitoring 12% versus non-therapeutic drug monitoring 7%, p = 0.456) and viral load detectable at birth (therapeutic drug monitoring 14% versus non-therapeutic drug monitoring 9%, p = 0.503). There were no instances of mother-to-child transmission. Therapeutic drug monitoring’s association with medication changes is postulated as partially causal in this cohort. There was no evidence of any association with improved control or reduced transmission of HIV to advocate routine therapeutic drug monitoring use.