Abstract
Twinning and placental fusion occur at a low frequency in species like humans and mice. They are linked to reduced birth weight and intertwin growth discrepancy with important consequences for perinatal survival. Despite this, little is known about the histological characteristics of the twin or fused placenta and how these relate to fetal growth. In this case report, we characterise the histological changes of a fused mouse placenta showing intertwin growth discrepancy. Our study demonstrates that morphological changes in the placental exchange and endocrine regions and elevated calcification levels may contribute to the intertwin growth discrepancy observed in mouse pregnancy.