I personally know of several cases.
So do I! There is a dangerous assumption that parents will seek to prevent an abortion once they find out about an underage/illegitimate pregnancy. It is frequently not true!
You're right. I worked in a crisis pregnancy center where a 15 year old came to us because she did not want to have her THIRD abortion. Her mother was a doctor, btw, and had arranged for the girl's first two abortions virtually on the spot - the first one was when the girl was 13.
We told her she was pregnant and she burst into tears and said she didn't want to have another abortion. We gave her as much information and sources of assistance as possible, but I doubt that once she stepped out our door, she had much choice in the matter. I'm sure Mother hauled her off to an abortionist buddy as soon as she got home that day.