Even if they're using contraception every time failure rates are still 96-98% per year for most contraceptives. Five years of regular intercourse puts you at 10-20% chance of pregnancy while in your early twenties. Even the life of brother Neal is better than no life as I'm sure he can attest.
Abuse rates in college educated single parent homes are not appreciably lower than in homes with a single parent without a college education according to any data that I can find. I'm not terribly familiar with that literature though. Perhaps you can point is all in the right direction.