SUMMARY: The umbilical cord is essential for fetal development, with its vessels undergoing continuous remodeling to sustain growth. Disturbances in vascular wall structure and extracellular matrix organization have been linked to impaired development and congenital malformations. However, systematic analyses of umbilical cord vessel histomorphometry and collagen maturation across gestational stages remain scarce. Ninety-seven human fetuses (51 normal, 46 malformed) were stratified into post-conceptional week subgroups (13–16, 17–20, 21–24, 25–28). Proximal cord segments were processed with Weigert’s resorcin-fuchsin and Picrosirius Red. Vessel and cord areas and wall thicknesses were measured with ImageJ. Collagen distribution was qualitatively assessed under polarized light. Data normality was tested by Kolmogorov-Smirnov; intragroup comparisons used Kruskal-Wallis with Dunn’s post hoc; intergroup comparisons used Student’s t or Mann-Whitney U tests; correlations were analyzed with Spearman’s rho. Significance was set at p < 0.05. In normal fetuses, all morphometric parameters positively correlated with gestational age (p < 0.001), including cord area (r = 0.502), vein area (r = 0.735), artery area (r = 0.725), and wall thicknesses. Both vein and artery cross-sectional areas and wall thicknesses increased significantly across intervals. For example, arterial wall thickness rose from 0.17 ± 0.07 mm at 13–16 PCW to 0.35 ± 0.09 mm at 25–28 PCW (p < 0.05). In malformed fetuses, only artery area (r = 0.392, p = 0.007) and arterial thickness (r = 0.570, p < 0.001) correlated with gestational age, while vein wall thickness and cord area showed no significant progression. Between groups, vein area was greater in malformed cords at 13–16 PCW (p = 0.0041), while at 17–20 PCW both vein and artery wall thicknesses were reduced (p = 0.0027 and p = 0.0003). No differences were observed at 21–28 PCW. Picrosirius Red revealed progressive collagen maturation in normal cords, contrasting with persistent disorganization and delayed maturation in malformed cords. Normal umbilical vessels exhibit predictable morphometric and collagen maturation patterns, while malformed fetuses demonstrate impaired remodeling, supporting cord histology as a potential marker of fetal pathology.

KEY WORDS: Umbilical cord; Fetal malformation; Vessel wall thickness; Elastic fibers; Collagen; Histomorphometry.

TEIXEIRA, A. R.; PIRES, L. A. S.; RÁFARE, A. L; RODRIGUEZ, B. C.; FONSECA JÚNIOR, A.; CHAGAS, M. A.; CHAGAS, C. A. A. & BABINSKI, M. A. Histomorphometric and qualitative analysis of umbilical cord vessels in normal and malformed human fetuses between 13 and 28 post-conception weeks. Int. J. Morphol., 44(2):404-413, 2026.