Can you request compassionate reassignment from Korea if your wife is pregnant back in the states?

Pregnancy is a normal event. Spouses are pregnant over deployments all the time. Unless there's an outstanding medical reason that your spouse needs you to be present, then it doesn't warrant a CR.

Nope. It's extremely rare and usually only if she is having a dangerous pregnancy. where her health is at risk.

The other answers here don't specifically answer your question. Yes, you can request a compassionate reassignment. However, like the others stated, the likelihood of it being approved is another matter. The chances are small, barring some unique circumstances (beyond simply your spouse being pregnant and your desire to be with your spouse).