Objective Pregnant women satisfaction with the Prevention of Mother-To-Child HIV Transmission services is an essential parameter in the determination of the quality of care and performance. This study aimed to measure the gap between pregnant women expectations of PMTCT services and perceptions of the actual PMTCT services and the relationship between their service gap scores and socio-demographic characteristics. Methods A cross-sectional descriptive study design was conducted from August to September 2020 on a sample of 105 participants. A pre-tested SERVIQUAL questionnaire was used to collect data and paired sample t-test, independent one-sample t-test, and one–way ANOVA was used to compare mean service gap scores. A p-value of < 0.05 was considered statistically significant. Results The overall mean gap score was (+ 0.31) indicating pregnant women perceived value of the quality of care of PMTCT services. The gap score in the 5 service dimensions was as follows: empathy (+0.49), tangibles (+0.43), assurance (+0.22), responsiveness (+0.20), and reliability (+0.19). Marital status (p-value 0.031) was the only social demographic characteristic associated with pregnant women service gap scores. Conclusion Overall, pregnant women perceptions of PMTCT services provided in the RCH clinic at KCMC were meet. Marital status was associated with the overall pregnant women service gap scores and perceived quality of care with PMTCT services. Pregnant women who were married had small service gap scores compared to either divorced or widowed or cohabiting women.