It's Alive

Whatever it is, it's alive, and deadly.

Diaper rash... turns into diaper rage.

The Davies baby... came out a little odd. It has a nasty habit of killing when it's scared. Which is pretty much all the time.

Followed by two sequels, It Lives Again and It's Alive 3: Island of the Alive, and a very poorly regarded remake.

Tropes used in It's Alive include:

• All There in the Manual: The novelization provided background to why the baby turned out so screwed up (Lenore had been using experimental fertility drugs shortly after she stopped taking birth control pills).
• Downer Ending: Frank manages to find an emotional connection with the baby, but the military kills it minutes later. Not to mention his wife has been driven insane due to the whole ordeal and there's more mutant babies being born all over the country.
• Enfant Terrible/Fetus Terrible
• Gorn