In this 1976 film, Rock Hudson plays a veterinarian who strikes a dog while driving during a rainstorm. He takes the dog to his lab to try and save it, but the situation quickly becomes more complicated as he realizes that the dog is pregnant and is too badly injured to survive. He tries to save the puppy fetuses, but they all die save one. It will die too, unless he uses an experimental growth hormone he's been working on. He save the pup, but it grows at an accelerated rate.
He discovers that if he treats puppy with the drug, its growth rare is accelerated, but off the drug the dog ages at a normal rate. The dog also seems to be of above average intelligence, but unbeknowst to the doctor the dog also has an evil viscous streak. He decides to try the same experiment on a human embryo.
He gets hold of a living 14 week-old human fetus and using his growth hormone is able to bring it to term in a matter of days. Unlike the puppy, the baby continues to age even without the treatment and in a matter of weeks she grown into Barbara Carrera. Like the puppy however, she also also has a vicious streak.
This is a long, dragged out movie that takes a long time getting anywhere. Roddy McDowall has a brief cameo that livens things up, but otherwise it really drags. It also never really addresses the ethical questions it raises. It was made two years before the first "test tube baby" was born, the perfect time for a thoughtful examination of these issues, but it dodges those questions to concentrate instead on being a slowly-building thriller. It fails on that count, too.