Psalm 139:14

I will praise You; for I am fearfully and wonderfully made: your works are marvellous; and that, my soul knows right well.

The placenta is responsible for working as a trading post between the mother’s and the baby’s blood supply. Small blood vessels carrying the fetal blood run through the placenta, which is full of maternal blood. Nutrients and oxygen from the mother’s blood are transferred to the fetal blood, while waste products are transferred from the fetal blood to the maternal blood, without the two blood supplies mixing.

So a baby’s blood belongs to itself and is unique.