Despite global advancements, pregnant women living with HIV in Nepal remain at risk for vertical transmission. This study examined demographic and clinical characteristics, antiretroviral therapy (ART) retention, and transmission outcomes among this population. A retrospective cohort analysis was conducted using data from Nepal's national electronic HIV register, including 322 women who became pregnant between 2020 and 2023. We analyzed sociodemographic profiles, clinical status at diagnosis, ART initiation timing, retention rates at 6, 12, and 24 months, and infant HIV status. The mean age was 26.9 years; over half (56.2%) were aged 25-39 years. Nearly 40% were illiterate, 87.6% unemployed, and 66.8% reported unsafe sexual behavior as the mode of HIV transmission. Over half (58.1%) were diagnosed prior to pregnancy, and 75.5% were in WHO Stage 1. ART began on the same day in 34.8% and within a week in 40.1%, with 56.8% already on ART during pregnancy. Retention was high: 96.9% at 6 months, 94.8% at 12 months, and 96.0% at 24 months. Vertical transmission occurred in 4.3% of pregnancies. Higher transmission rates were observed among younger mothers (6.9%), Dalit women (11.5%), those in advanced HIV stages (11.1%), with delayed ART initiation (8.6%), high viral loads (13.3%), and home deliveries (17.6%). In Nepal, approximately 1 in 23 infants born to women living with HIV still acquire the infection. Strengthening early diagnosis, improving ART uptake, and addressing disparities in care especially among high-risk groups are essential to eliminating vertical transmission and improving maternal and child health outcomes.