Dr. Alex Hesse, an Austrian research geneticist, portrayed by Arnold Schwarzenegger, along with his OB/GYN colleague Dr. Larry Arbogast, played by Danny DeVito, is on a quest to revolutionize fertility with their newly developed drug, "Expectane." This innovative medication aims to significantly reduce the odds of miscarriage, addressing a critical issue that Alex believes stems from the female body mistakenly rejecting embryos as foreign invaders. In his words, “The body mistakes the embryo as unwanted foreign substance and creates antibodies to fight and reject it.” The duo's previous tests on a chimpanzee have shown promise, as the animal, after being treated with Expectane, successfully progressed to a seven-month pregnancy despite its previous miscarriage history.
However, their ambitions take a hit when the head of the University review board, Noah Banes, breaks the disappointing news that the FDA has rejected their drug following their presentation. With no approval in sight, Alex's research hopes hang in the balance. Banes insists that Alex clear out his lab, a request Alex firmly refuses, while Larry desperately pleads that they compromise, reminding Banes of their substantial investment that totals $300,000. Meanwhile, a new competition arises in the form of geneticist Dr. Diana Reddin, who brings her Cryogenics project to the university, further complicating matters as she occupies the lab space that Alex must vacate.
Feeling defeated, Alex contemplates a fresh start in Europe without a lab or funding. However, Larry proposes an audacious idea: they can still move forward with their experiment with financial backing from a Canadian firm, provided they can find a volunteer. Although Alex expresses skepticism about a pregnant woman willingly taking an unapproved drug, Larry cleverly suggests that they can simply omit the volunteer’s gender. They move forward with a shocking plan where, against all odds, Alex decides to undergo the experimental procedure by fertilizing a frozen egg, secretly labeled “Junior” by Diana, and implanting it into himself.
As Alex's unexpected pregnancy progresses, he experiences a whirlwind of side effects, from morning sickness to the emotional upheaval of impending fatherhood. The process amusingly transforms Alex's life as he finds himself discussing maternal topics with increasing fervor and frequently bonding with Diana, whose empathy for his situation deepens. An intriguing tension builds as Alex's growing connection with Diana intersects with the pressures of secrecy and ethical considerations surrounding their unconventional experiment.
As proprietary interests and rivalries emerge, especially from Banes who suspects Alex is engaged in unauthorized human experimentation, the stakes become dangerously high. Amid the chaos, Larry attempts to woo Diana, and twin-father dynamics develop between Alex and Larry, who ultimately become reluctant collaborators in this extraordinary journey of conception.
In a gripping and comedic climax, as Alex nears the delivery of his baby, the plot thickens with media attention and university politics, leading to an urgent and clandestine c-section. Remarkably, Alex gives birth to a healthy baby girl, aptly named Junior, amidst the chaos and impending crisis of Banes's ambition for recognition. The narrative culminates in a surprising reunion of the families and the promise of new life, with both Alex and Larry receiving personal rewards for their unorthodox yet heartfelt drive toward parenthood.
One year later, as the families come together to celebrate Junior's first birthday alongside Jake, the son of Angela, played by Pamela Reed, and Larry, new life—and laughter—utterly transform their intertwined futures. With romantic developments leading to further pregnancies on the horizon for both couples, the sense of camaraderie and shared challenges reflect the bountiful joys of parenthood that unexpectedly brought them together.
