Well it looks like the WT was slowly moving away from the blood ban going back to the 1990's but not sure of some things I have read concerning thier comments about blood moving through the Placenta?
That some protein fractions from the plasma do move naturally into the blood system of another individual (the fetus) may be another consideration when a Christian is deciding whether he will accept immune globulin, albumin, or similar injections of plasma fractions. One person may feel that he in good conscience can; another may conclude that he cannot. Each must resolve the matter personally before God. – The Watchtower 06/01/1990 p. 30
Then AJWRB.org says this
The Watchtower is clearly aware that the basis for their major/minor blood component policy is completely without merit. All major blood components also pass through the placental barrier as we have demonstrated.
Yet my research seems to indicate that no blood of the mother passes through the placenta barrier to the fetus, so who is correct or are they both wrong??