to frame an argument of similarity (?)
Unlike a kidney transplant or a metal buttress for a broken bone, BT blood is absorbed by the body thereby ingesting it.
My examples are not highlighting relationships but pointing out that when an act such as killing is defined as murder in the Bible and prohibited, the Bible also clearly defines when killing is not prohibited and allowed. Therefore, although there is a difference between eating blood and using blood for medical reasons, the Bible does not sanction any medical use of blood or other use of blood except for ritual, so the Decree ( according to the latest JW commentary ) not only refers to eating blood but also involves medical use in a blood transfusion.
(All of the transfused blood in a BT might not be absorbed right away but similar to the y chromosomes you mentioned that showed up in the blood stream of the mother (assumed true) any trace blood of the fetus will be absorbed or ingested in time by the mother with no evidence of y chromosomes.)