Expressions (phrases, clauses, etc.), Noun
marriage due to unintended pregnancy; shotgun wedding
Abbreviationsee できちゃった結婚
できちゃった婚のため身内と大学の友人2人しかよばない地味婚にするそうです。It seems as it was a shot-gun wedding so they're having a quiet wedding with only family and a couple of friends from university invited.
Also written 出来ちゃった婚【できちゃったこん】