No, really. Arnold plays Dr. Alexander Hesse who, with his partner Dr. Larry Arbogast (Danny DeVito), develops a drug that is supposed to help against miscarriages. After being denied research funding and a test subject, Alexander agrees to carry the baby after some convincing from Larry. Although it was initially to be a three-month test, he ends up carrying the baby to full term.
No, really. He gives birth and everything. We get to see him all the way through the pregnancy. It's played mostly straight, but at least gives a somewhat interesting Character Development by breaking Alexander out of his shell. The baby also has a mother, Dr. Diana Reddin (Emma Thompson), who had (unknowingly) donated the ovum. Alexander and Diana start an unconventional family by the end.
This film provides examples of:
- Babies Ever After: Two live births and counting by the end.
- Hand Wave: In order to make the Mr. Seahorse premise a little more palatable, one character who pulls Dr. Hesse's (unlabeled) file notes that he's being given massive doses of various female hormones, the kind and quantity one would usually see given to someone preparing for a sex-change operation. In Real Life, something like this probably would be necessary, though so far the preliminary research and experimentation to figure all of this out hasn't been done, for lack of both sufficiently motivated researchers and volunteers to bear the unknown risks.
- Here We Go Again!: In the epilogue, when Angela (Larry's wife) thinks of having another baby but doesn't want to go through all the pregnancy again and Alexander says she doesn't have to. Then they all stare at Larry, who catches on and says "oh no." And runs off with Alexander chasing after him saying it won't be that bad.
- Hot Scientist: Diana. Overlaps with Cute Clumsy Girl. Diana sees Alex as a male version of this.
- Mister Seahorse: The Movie.
- Mood-Swinger: Due to being pregnant, Alexander starts experiencing this. Notably, he cries while watching a romance.
- Professor Guinea Pig: Yep... although in this case, it's a mutual partnership deal with two professors.
- Spiritual Successor: To Twins.
- The film would get one of its own in the form of Juno, directed by Ivan Reitman's son.
- Wholesome Crossdresser: Perhaps one of the most hilarious parts in the whole film is Arnold donning a dress to enter a home for expecting mothers, and explaining his physique to the other mothers as a result of having supposedly been shot up with male hormones while competing in the Olympics for East Germany, which then produced quite a lot of very mannish-looking muscular female athletes such as... himself.