We learned about this in a class I took in college a couple years ago.
I did some Google-searching, and I wanted to remember it, so it's going here.
Here's the Wikipedia article on the "Twilight sleep":
Twilight sleep article
The drug was scopolomin (and morphine, at least according to Wikipedia), and it was used as an anesthetic in the early 1900s for women in childbirth.
This is the New York Times article (1914) about the controversy surrounding "twilight sleep":
Deny Insanity Is Due To 'Twilight Sleep'
It made women forget the pain, on the theory that if they don't remember, it didn't happen. But they were awake and aware when it was happening, or presumably in a "twilight sleep"; but they were still able to push, and all that.
It also made them crazy.
I will leave you with this, in case you don't feel like reading the articles:
"The next thing I knew I was awake [...] and then I thought to myself "I wonder how long before I shall begin to have the baby," and while I was still wondering a nurse came in with a pillow, and on the pillow was a baby, and they said I had had it—perhaps I had—but I certainly can never prove it in a courtroom." ("TWILIGHT SLEEP; Is Subject of a New Investigation". The New York Times. 1915-01-31. http://query.nytimes.com/gst/abstract.html?res=9E05EED8113EE733A05752C3A9679C946496D6CF. Retrieved 2008-08-05.)