I've not heard of hormone washing in the womb, but I can't imagine it's good news.
I haven't heard of this in relation to humans @ReneBumsWombats , but I have in relations to puppies.
In a litter of pups, if there is a large number of puppies of one sex (eg as with our spaniel 11 pups, 9 males and 2 females), and the minority sex pups are between the majority ones, they can become affected by the hormones of the other sex. Our little cocker bitch, for instance, lifts her leg to pee like a male dog (a proper "pee-up-the-wall", not just a "don't-want-a-wet-paw" lift). I assume that this happens with other animals which have larger numbers of babies at a time. This is because a bitch's uterus is shaped like a "y", with two horns, and the hormones are pretty much free flowing even though each pup has its own amniotic sac. (I don't pretend to understand the mechanics of this.)
As far as I know (but I'm not an endocrinologist or a biologist so could well be wrong) this is unlikely to happen in humans because we don't tend, even in a multiple pregnancy, to have enough babies of one sex for the concentration of their hormones to "overwhelm" the baby of the other sex.
It will be interesting to see how androgenised the babies of transmen are, when their mothers - sorry - gestational parents have been pouring testosterone into herself form months or years. This social experiment isn't just affecting the safety of women it could very well be affecting the health and mental well-being of newborn infants.