How urea moves from the foetus blood to the mother blood?

Urea moves from the fetus's blood to the mother's blood primarily through the placenta via diffusion. As the fetus metabolizes proteins, urea is produced and enters the fetal bloodstream. The concentration gradient allows urea to diffuse across the placental membrane into the maternal circulation, where it can then be excreted by the mother's kidneys. This process helps maintain proper nitrogen balance for both the fetus and the mother.