The National Hospital Insurance Fund (NHIF) of Kenya was upgraded to improve access to healthcare for impoverished households, expand universal health coverage (UHC), and boost the uptake of essential reproductive, maternal, newborn and child health (RMNCH) services. However, premiums may be unaffordable for the poorest households. The Innovative Partnership for Universal Sustainable Healthcare (i-PUSH) program targets low-income women and their households to improve their access to and utilization of quality healthcare, including RMNCH services, by providing subsidized, mobile phone-based NHIF coverage in combination with enhanced, digital training of community health volunteers (CHVs) and upgrading of health facilities. This study evaluated whether expanded NHIF coverage increased the accessibility and utilization of quality basic RMNCH services in areas where i-PUSH was implemented using a longitudinal cluster randomized controlled trial in Kakamega, Kenya. A total of 24 pair-matched villages were randomly assigned either to the treatment or the control group. Within each village, 10 eligible households (i.e., with a woman aged 15-49 years who was either pregnant or with a child below 4 years) were randomly selected. The study applied a Difference-in-Difference methodology based on a pooled cross-sectional analysis of baseline, midline and endline data, with robustness checks based on balanced panels and ANCOVA methods. The analysis sample included 346 women, of whom 248 had had a live birth in the 3 years prior to any of the surveys, and 424 children aged 0-59 months. Improved NHIF coverage did not have a statistically significant impact on any of the RMNCH outcome indicators at midline nor endline. Uptake of RMNCH services, however, improved substantially in both control and treatment areas at endline compared to baseline. For instance, significant increases were observed in the number of antenatal care visits from baseline to midline (mean = 2.62 to 2.92) p < 0.01) and delivery with a skilled birth attendant from baseline to midline (mean = 0.91 to 0.97 (p < 0.01). Expanded NHIF coverage, providing enhanced access to RMNCH services of unlimited duration at both public and private facilities, did not result in an increased uptake of care, in a context where access to basic public RMNCH services was already widespread. However, the positive overall trend in RMNCH utilization indicators, in a period of constrained access due to the COVID-19 pandemic, suggests that the other components of the i-PUSH program may have been beneficial. Further research is needed to better understand how the provision of insurance, enhanced CHV training and improved healthcare quality interact to ensure pregnant women and young children can make full use of the continuum of care.