The journal Sexual Health recently published a study on unintended pregnancy. According to the study's abstract, 51 percent of women who reported an unintended pregnancy went on to experience at least one other unintended pregnancy.
Other factors also contributed to multiple unintended pregnancies: one's race (women who are black or Hispanic are more likely to experience multiple unintended pregnancies), having been born to a mother who was under 18 when she gave birth, and young age of first sexual experience (whether consensual or not).
The abstract didn't disclose whether any of these factors coincided with income or insurance coverage. I'd be interested to see how those factors stack up.