You are perfectly in your right to question. I don't have an issue with it and just want to learn and know the truth as well.
I did read it somewhere, and remember discussing it with my wife as well, because I am generally very sceptical of pharmaceutical drugs, and she said my son reacts well to Loratadine. I should have posted the source, but don't know why I didn't. I tried again to find the quote, but can't remeber where it was, or it was maybe a radio interview.
Anyway, the closest I could find again, was this quote, http://raypeat.com/articles/hormones/h1.shtml
Histamine mimics estrogen's effects on the uterus, and antihistamines block estrogen's effects (Szego, 1965, Szego and Davis, 1967).
So I stand corrected, but it could also possibly have been my interpretation of all antihistamines being anti estrogen like. Cyproheptadine generally causes side effects like drowsiness and Loratadine do not do this to my son, which is why my wife gives it to him when needed.
As to your quoted study, I cannot comment, as there is too little information available regarding dosage and also rats vs humans. (even if it were true, luckily my son is not in the uterus anymore !