Corrected entry: At the end of the episode the female child molester reveals that she has just learned that she's pregnant with her victim's child. However, earlier in the episode (several weeks prior in the episode's time span), she underwent surgery. A Pregnancy test is part of a standard pre-op workup for all women of child-bearing age. She would have learned about her pregnancy then. Obviously, this was altered for the "end of the episode" dramatic effect.
Corrected entry: The doctor speaks with Olivia about how the girl is older because she doesn't have wisdom teeth and people get them when they are adults. This is what turns the investigation. Although, that is sometimes true, it is not ALWAYS true. My wisdom teeth were removed when I was 16, and I know of friends who have also had them removed before adulthood. So to base it primarily on that would not have been sound.