Fools Rush In

Fools Rush In is a 1997 romantic comedy starring Matthew Perry and Salma Hayek.

Alex (Perry) and Isabel (Hayek) get more than they bargained for from a one night stand. When Isabel finds Alex to let him know she's pregnant the two take the next logical step -- they get married on the Vegas strip that very night. But the romantic notion fades quickly and they learn that being married to someone you barely know is much harder than they thought, especially with a baby involved.

Tropes used in Fools Rush In include:

But We Used a Condom: Alex's reaction to Isabel saying she's pregnant.

Alex: But I used a condom... I used a lot of condoms.
Isabel: Yeah, well, one of them didn't work.

Fourth Date Marriage: Actually their second date.
Good Girls Avoid Abortion: Isabel tells Alex that she's made the only logical decision. Alex assumes she means abortion and is instantly relieved. Isabel is horrified and tells him that the only possible decision for her is to keep the baby.
Instant Birth, Just Add Water: Isabel's water breaks from the shock of Alex walking out in front of her car. By the time the ambulance arrives, she's already delivered their daughter.
My Sister Is Off-Limits: Isabel's brothers are very protective and Alex suspects they may be plotting to kill him.
Papa Wolf: Isabel's father drives his truck into freshly poured concrete and threatens Alex with a baseball bat when he finds out what has happened.
Viva Las Vegas: Alex and Isabel get married on the strip after she tells him about the baby.