In this study, we aimed to reveal whether the medial longitudinal arch is formed in the intrauterine period and the structural features of the medial longitudinal arch. The study was conducted on 146 feet of 73 fetuses (38 male, 35 female) aged between 15 and 40 weeks of gestation. The fetuses were grouped by trimesters. The footprints taken were photographed with a millimeter ruler, and the development of the medial longitudinal arch was examined on footprints based on the Clarke index, Chipaux-Smirak index, and Staheli index. In Clarke index and Staheli index, it was observed that the arch height was normalized in the transition from the second trimester to the third trimester, the arch decreased in the transition to full-term, and the rate of pes planus increased. All indices detected pes planus by 81.81% in the full-term period. The rate of pes planus determined according to Clarke index and Staheli index, especially in the third trimester period, was 6.94% and 11.11%, respectively. We have provided a perspective on how the development of the medial longitudinal arch is shaped in the intrauterine period. Based on the results of study, we consider that the data on the medial longitudinal arch, especially in the third trimester period, may be more significant. In the evaluations made from the footprints of premature infants in the intrauterine third trimester period in the future, a study, in which infants detected with pes planus can be followed up and the development of their medial longitudinal arch is evaluated, can be conducted.