Digital assessments of caput succedaneum are subjective; however, caput succedaneum can also be expressed as ultrasound measured skin–skull distance (SSD). In this study, we aimed to compare the clinical and ultrasound assessment of caput succedaneum (caput) in nulliparous women in the first stage of labour. Furthermore, we aimed to investigate the repeatability of ultrasound measurements. We observed a significant but low correlation between clinical and ultrasound assessments (Kappa value 0.29; P < 0.01). Interobserver repeatability for SSD showed an intraclass correlation coefficient of 0.96 (95% CI, 0.93–0.98). The mean difference for the caput measurements was −0.4 mm (95% CI, −0.85 to 0.05), and limits of agreement were −3.44 to 2.64 mm. We conclude that ultrasound measured SSD is an objective expression of caput with significant correlation with clinical assessment.