[The_voice_of_reason]

Source: Merriam-Webster Medical Dictionary, © 2002 Merriam-Webster, Inc.


metabolism

\Me*tab"o*lism\, n. (Physiol.) The act or process, by which living tissues or cells take up and convert into their own proper substance the nutritive material brought to them by the blood, or by which they transform their cell protoplasm into simpler substances, which are fitted either for excretion or for some special purpose, as in the manufacture of the digestive ferments. Hence, metabolism may be either constructive (anabolism), or destructive (katabolism).


Since the fetus needs the mother to bring it the nutrients it doesn't have and independent metabolism. Just because it can utilize nutrients doesn't mean it has an independent metabolism.