Can a 20-year-old go to jail for getting a 15-year-old pregnant?

In the United States, yes. In the United Kingdom, yes. In most (but not all) other countries, yes. However, this does not mean the man WILL go to jail. If the girl's parents choose to press charges, (or if the state laws require it) though, it is very tough to avoid a conviction and a long prison sentence (up to life in jail). The ages of consent range from 16 to 18, meaning a twenty-year old is almost universally forbidden from having sex with a minor. Check with the laws of your state or province to be sure. If this escalates to a worse situation, contact an attorney and discuss your legal options.

In the meantime, work with the girl's parents to support her and your child. Don't let one big mistake turn into a much bigger one; stay involved in your child's life.

It depends on the state. In most states the age of sexual consent is 16 (in some it's higher). If an adult has sex (even if it wasn't 'forced') with someone under the age of sexual consent then they have commited a crime. They can be charged, tried, and convicted. Once that baby is born, it will be very easy (with a DNA test) to prove beyond any doubt that this man is guilty. Even if the girlfriend or her family didn't want to press charges, the state can still chose to press charges.

With a 5-year age difference, and the fact that the elder of the pair is over 18, you have to look at statutory rape. Statutory rape does not take consent into consideration. Different states have different definitions of the age limits and age differences, and it's a serious offense. If the prosecutor is angry, the elder of the pair can get up to life in prison! And if and when released from prison, he (or she) goes on the sexual-offfender list, with all the restrictions that carries.

for England and Wales

The age of consent in England and Wales is 16. The offence committed is 'Unlawful Sexual Intercourse' and does carry a prison sentence HOWEVER, because of the girl's proximity to the age of consent and the young man's youth, as long as there was no evidence of force, it is likely that he may receive a Police caution (and as a result, lose the chance to work with children in the future).