Abstract Objectives Frontline workers (FLWs) deliver essential nutrition services to reduce maternal undernutrition in India, but coverage and quality remain sub-optimal. Alive & Thrive aimed to strengthen delivery of interpersonal counselling, community mobilization and micronutrient supplements through the government antenatal care (ANC) platform in UP. We studied pathways through which the nutrition-intensified ANC (I-ANC) was intended to impact FLWs capacity, knowledge, and service delivery, compared to standard ANC (S-ANC). Methods We used a cluster-randomized design with cross-sectional surveys at baseline (2017) and endline (2019), ∼500 FLWs per survey. Differences between I-ANC and S-ANC were compared along six impact pathway components (training, availability of materials, supportive supervision, knowledge, service delivery, and counselling content) using mixed-effects regression adjusted for clustering. Results Training exposure was higher in I-ANC than S-ANC (9 percentage points, pp). Nutrition training topics were low-moderate (30–60%) in both arms. Job aids were more available in I-ANC (70–80%) than S-ANC (30–40%). Supply of iron-folate and calcium supplements were low in both arms, with 10–50% having stock-outs. FLWs in I-ANC were more likely to receive supervision visits (7 pp), but gaps remained in both arms. Compared to S-ANC, FLWs in I-ANC had higher knowledge on diet diversity (6 pp), adequate intake (10 pp), iron-folate (10 pp) and calcium supplements (30 pp), pregnancy weight gain (20–30 pp), and early breastfeeding (5 pp), but similarly low knowledge of exclusive breastfeeding. ANC check-ups by FLWs were 20 pp higher in I-ANC. FLWs in I-ANC did more counselling on adequate diet, supplements, and weight gain (10–20 pp). Counselling on diet diversity and breastfeeding were low in both arms. Conclusions Health systems strengthening efforts helped improve the delivery of maternal nutrition interventions in antenatal care in this context, but gaps remain. Several health system elements along the program pathway – supply chain management, training, supervisory practices – require strengthening to further improve FLW knowledge and nutrition service delivery. Funding Sources Bill & Melinda Gates Foundation, through Alive & Thrive, managed by FHI 360.