File:The Terror Within (1989)

Description
It's the post-apocalypse, and the world has been changed by "the accident," a chemical warfare experiment gone awry. At an isolated subterranean complex, a group of people survives because they were able to get the antidote for the illness. They rescue a surface survivor from the gargoyles, who unfortunately had time to impregnate her, and when the "baby" is born and escapes into the ventilation ducts, they begin experiencing an attrition problem.

Fun Alien clone from the late 80s starring the always hot Andrew Stevens and features some fairly solid effects work