Beyond attendance: facility-level variations in the delivery of essential antenatal care interventions during routine group antenatal care implementation in Tanzania: a secondary analysis

High antenatal care (ANC) attendance does not necessarily ensure receipt of the full package of recommended interventions. Although Group Antenatal Care (G-ANC) may improve service utilization and quality, little is known about facility-level variation in implementation when integrated into routine health systems. We assessed variation in the delivery of essential ANC interventions within a routine G-ANC program in Geita Region, Tanzania. We conducted a secondary analysis of routinely collected implementation data from the Mlinde Mama Project between January 2023 and August 2024. No sampling was undertaken; all 5,936 pregnant women enrolled in G-ANC across six public health facilities (two dispensaries, two health centers, and two district hospitals) during the study period were included. Coverage of 12 ANC indicators was assessed. A composite facility performance score was calculated as the mean coverage of nine selected indicators. Descriptive statistics summarized coverage, and Pearson’s chi-square tests assessed differences across facilities. A total of 5,936 pregnant women were enrolled into 149 G-ANC cohorts at the implementation sites during the study period. ANC4 + coverage ranged from 90.2 to 95.0%, facility delivery from 94.1 to 97.7%, and malaria testing from 91.5 to 95.5%, while blood pressure monitoring was 100% across all facilities. Greater variation was observed for preventive and diagnostic interventions: IPTp3 + coverage ranged from 60.1 to 86.3%, iron–folate supplementation from 75.0 to 92.7%, HIV and syphilis testing from 59.9 to 95.0%, and urine testing from 30.1 to 62.7%. Composite performance scores ranged from 80.1 to 91.9%, with Bwanga Health Center ranking highest and Butengorumasa Dispensary lowest. Health Centers demonstrated the strongest overall performance across most indicators, and coverage of the nine indicators included in the composite score varied significantly across facilities ( p < 0.05). Women enrolled in routine G-ANC had high ANC attendance, but delivery of several essential interventions varied substantially across facilities. These findings highlight gaps between service utilization and effective coverage and support monitoring ANC content alongside attendance. Facility-level performance monitoring, supportive supervision, and continuous quality improvement may help address implementation gaps and strengthen comprehensive ANC delivery.