In Bed with Santa (1999)

Sara invites her ex-husbands and their new families to celebrate Christmas with her and her husband Janne. Sara has always wanted to have a baby with Janne, and at the dinner table she reveals the news: she's pregnant. The only problem is that Janne had a vasectomy two years ago, without Sara knowing it. The secret starts to spread among the guests, and in no time everyone knows but Sara. The party heads for a complete disaster. Who's the real father?