The Church knew realized it from the beginning, they were led astray shall we say. I can give you more but I'd say God's word would be the deciding factor for those of faith though the Didache and many other early and prominent Christians did not adhere to Augustines views.
Stuff happens.
Which would of course indicate that no new bio-science was necessary for the determination. Nor do I believe Augustine and Thomas among many others during that time and for the next 1200 years were evil. They were some of the best minds within the Church. Suffice it to say that for more than a millennium, it was an arguable position, just as it is today.
Yes, many did not support that position, just as some Catholics and other Christians don't support the Church's position today.
The beat goes on...
I'm convinced that the decisions they made were made with the knowledge they had at the time, and to protect the women who miscarried or had a late period.
All too often, these arguments are made by the same people who ridicule religion for insisting that the sun revolved around the earth. As though none of the geocentrists were the equivalent of scientists. And, they're hoping we don't remember the way Medicine resisted the germ theory and the way that Semelweis was treated by the hierarchy at that time. Or, more recently, the difficulty in convincing Medicine that folic acid was vital to neural tube development, that breast feeding really is best, that heart disease is really due to a bacterial infection and that cervical cancer is an STD.
We should all remember that science develops better tools, with finer measurements all the time. Knowledge simply increases, often before we know what we're doing. It's hard to let go of the old pardigms -- especially if someone's reputation (or Lord forbid!) research grant is at risk.
We now know what happens when a sperm and an oocyte fuse. We especially know which embryos in the Petri dish are alive and which are not embryos or which are not dividing.
Extrapolating from "water" in the womb that can't be measured or verified to "water" in the lab - petri dish or, soon, the artificial uterus - after a deliberate act of creation is simply wishful thinking. And it goes against scientific knowledge.