Background: HIV-infected women risk sexual and perinatal HIV transmission during conception, pregnancy, childbirth, and breastfeeding. We compared HIV-1 RNA suppression and medication adherence across periconception, pregnancy, and postpartum periods, among women on antiretroviral therapy (ART) in Uganda. Methods: We analyzed data from women in a prospective cohort study, aged 18-49 years, enrolled at ART initiation and with $1 pregnancy between 2005 and 2011. Participants were seen quarterly. The primary exposure of interest was pregnancy period, including periconception (3 quarters before pregnancy), pregnancy, postpartum (6 months after pregnancy outcome), or nonpregnancy related. Regression models using generalized estimating equations compared the likelihood of HIV-1 RNA ≤400 copies per milliliter, <80% average adherence based on electronic pill caps (medication event monitoring system), and likelihood of 72-hour medication gaps across each period. Results: One hundred eleven women contributed 486 person-years of follow-up. Viral suppression was present at 89% of nonpregnancy, 97% of periconception, 93% of pregnancy, and 89% of postpartum visits, and was more likely during periconception (adjusted odds ratio, 2.15) compared with nonpregnant periods. Average ART adherence was 90% [interquartile range (IQR), 70%-98%], 93% (IQR, 82%- 98%), 92% (IQR, 72%-98%), and 88% (IQR, 63%-97%) during nonpregnant, periconception, pregnant, and postpartum periods, respectively. Average adherence,80% was less likely during periconception (adjusted odds ratio, 0.68), and 72-hour gaps per 90 days were less frequent during periconception (adjusted relative risk, 0.72) and more frequent during postpartum (adjusted relative risk, 1.40). Conclusions: Women with pregnancy were virologically suppressed at most visits, with an increased likelihood of suppression and high adherence during periconception follow-up. Increased frequency of 72-hour gaps suggests a need for increased adherence support during postpartum periods.