Semi-parasitic nature of placental mammal in-uteral development?

Question

I'm just curious about this.

With placental mammals, does the growing young function as a parasite or does the mother's body re-route nutrients to the placenta on its own?

Not looking to offend any mothers btw.

Answer 1

The foetus acts like a parasite, in some things. With Iron stores, it will take iron from the mother, to the point of making her anaemic. Nutrients such as glucose move freely across the placenta. Oxygen is sucked off the haemoglobin at the placenta/uterus interface by Haemoglobin F (HbF), which has a higher affinity for oxygen than adult haemoglobin (HbA).
Very efficient parasites, it doesn't stop until they leave home.
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Answer 2

Calcium needs by the fetus are an example of this.

Let's say there is a pregnant teenager. Her skeletal system isn't fully developed yet since she is still growing. If her diet or calcium supplementation is not adequate (maybe she is eating too much junk food), the fetus will look for available sources of calcium (for its own skeletal system) by removing it from the teenager's bones. As a result, the mother is now at a higher risk for bone fractures.