Abstract
BACKGROUND: A proper placentation is required for establishment and continuity of pregnancy. In sheep, placentomes are unique structures that enable nutrition and gas exchange between the mother and the foetus. Although placentomes are dynamic formations, there is limited knowledge of changes in placentomes during pregnancy. OBJECTIVE: This study aimed to identify changes in sheep placentomes in the second and third trimesters of pregnancy using both macroscopic and microscopic methods. METHODS: This study investigated 14 healthy cross-breed Hamdani sheep placentomes, comprising seven second and seven third trimesters of pregnancy. The histomorphometric analysis included measurements of capillary number and area in cotyledonary and caruncular regions, while morphometric assessments encompassed placentome dimensions such as number, length, width, and depth. RESULTS: Placentomes were oval and circular in shape in the second and third trimesters. In the second trimester, they were observed as concave structures with thick edges, whereas in the third trimester, they were determined as thin-edged structures with a slight depression in the centre. In the third trimester, foetal and maternal tissues became more intertwined with increased branching of foetal villi and maternal crypts. Placental hematomas and erythrocytes in the cytoplasm of trophoblast cells were more prominent in the third trimester. Statistical analysis revealed no difference in placentome number between the second and third trimesters. However, the dimensions (length, width, and depth) of placentomes were greater in the third trimester compared to the second trimester (p < 0.001). Additionally, while there was no difference in the number of cotyledonary versus caruncular capillaries in the second trimester, cotyledonary capillaries outnumbered caruncular capillaries in the third trimester (p < 0.001). Furthermore, both cotyledonary and caruncular capillary areas increased in the third trimester compared to the second trimester, with the caruncular capillary area being consistently higher than the cotyledonary capillary area in both trimesters (p < 0.05). CONCLUSION: This study underscores the substantial structural and physiological transformations of placentomes in the second and third trimesters of pregnancy in sheep. These adaptations facilitate efficient flow exchange between the foetus and mother, highlighting the dynamic nature of placental development during late gestation.