{ "background": "Maternal mortality remains a critical public health challenge in sub-Saharan Africa. While access to care has improved, the quality of services is a decisive yet under-evaluated factor influencing health outcomes. Longitudinal assessments of service quality are scarce.", "purpose and objectives": "This study aimed to evaluate longitudinal trends in maternal health service quality and to quantify disparities between facility types and geographical regions over a multi-decade period.", "methodology": "We conducted a longitudinal analysis of nationally representative health facility survey data. Service quality was measured using a composite index of structural, process, and outcome indicators. Trends and disparities were analysed using a linear mixed-effects model: $Y{it} = \\beta0 + \\beta1 Tt + \\beta2 Xi + ui + \\epsilon{it}$, where $Y{it}$ is the quality score for facility $i$ at time $t$, $T$ is time, $X$ represents facility/region covariates, and $ui$ is the facility random effect. Robust standard errors were used for inference.", "findings": "Overall quality scores showed a significant positive trend (p<0.001). However, a pronounced and persistent disparity was observed, with private facilities scoring 15.2 percentage points higher on average than public facilities (95% CI: 12.8 to 17.6). Regional inequality, though narrowing, remained statistically significant.", "conclusion": "Despite aggregate improvements, systemic inequities in service quality between public and private sectors endure, potentially undermining equitable maternal health gains.", "recommendations": "Policy must prioritise targeted quality improvement in public facilities and strengthen regulatory frameworks to ensure minimum standards across all providers. Future research should investigate the drivers of the public-private quality gap.", "key words": "maternal health, service quality, health systems, equity, longitudinal study, sub-Saharan Africa", "contribution statement": "This study provides the first multi-decade, national-level analysis of maternal health service quality