Histological Observations of the Developing Human Fetal Humerus at Different Trimesters of Pregnancy

Abstract

Background: Although femur length is the preferred method for fetal age assessment, the humerus is sometimes the right choice, especially in the second half of pregnancy. Fetal bone development significantly impacts adult bone quality and senescent bone disorders, including osteoporosis. Purpose of the study: The present study aimed to ascertain the histological changes in the human fetal humerus across the three trimesters. After the institutional ethical committee clearance and parent consent, the study was carried out on stillborn or medically terminated human fetuses from the 10th to the 32nd week of intrauterine life. Results: First trimester: The primary bone collar appeared with the primary ossification center, marked by more vascular invasion and a pool of mesenchymal cells. Trabeculations begin from the bony collar and insignificant periosteum. Second trimester: The changes showed longitudinal growth of periosteal bone towards the proximal and distal ends of the growing bone. Growth plate with distinguished zones and gradual fusion of epiphysis with growth plate were observed. Third trimester: Trabeculation number and thickness increase with calcification. Towards the third trimester, the marrow cavity with increased and prominent trabeculations is consistent. Conclusion: Understanding normal microstructural and cellular events chronologically is an ideal platform for future studies to develop cell-based or cell-targeted therapies for adult bone disorders, traumatic bone injuries, or bone engineering. KEYWORDS: Histology, Developing Bone, Humerus, Fetuses, Embryology.