The only thing creepier and more dangerous than the Enfant Terrible. The Fetus Terrible hasn't even been born yet, but will become The Antichrist or a demon prophesied to bring about The End of the World as We Know It once it escapes from its womb. The woman carrying this (often literally) hellborn spawn is usually an innocent, unwittingly impregnated by the Devil himself, and the other characters have to race to prevent the birth or stop the child from becoming the ultimate Enfant Terrible. Occasionally this can result of a perfectly normal pregnancy Gone Horribly Wrong pre or post conception, where the issue can be a mutant, Hybrid Monster, Undead Child or some other abomination. This trope can also overlap with Body Horror, especially if the mother knows what's growing inside her.
After being raped by a newly-demonic Griffith, Casca gives spontaneous birth to one of these in Berserk, which is actually the unborn child of her and the protagonist Guts, who was conceived as a normal baby but was corrupted by the aforementioned rape. It's hideously malformed, teleports away if threatened, and has a certain amount of control over the demons that constantly come after her. However, it's only terrible in appearance: the thing is apparently mindless, yet drawn to it's parents like all children, and is willing to protect its mother. Eventually it merges with an egg-bodied demon, and Griffith is reborn through it.
Ganishka's demon soldiers, which are created by dropping pregnant women into a pool of liquid from captured Apostles and then burst from their mother's stomachs Alien style could count too. Trolls appear to be all male, who breed by raping human females, though I suppose consensual sex is possible even if the babies also comes out Alien style.
Yuca Collabel from Immortal Rainresurrects himself this way. Specifically, after his surrogate mother is unwittingly artificially inseminated with him, he rapidly grows to term in two months, causing his mother's stomach to get so huge that she couldn't walk. Why does she get so big? Because he's already aged to the form of a prepubescent boy in utero. Unsurprisingly, when she goes into labor, instead of taking the usual route, he just bursts out Aliens style.
Hao from Shaman King. His regular rebirth through conception is treated as an Anti-Christ thing by his clan. They have a special 'kill the infant' thing around the time of the Shaman Fight because one of them will be him.
Pinoko in Black Jack started out as a fetal mass of underdeveloped flesh with psychic powers, incrusted as a huge parasitic tumor in the body of a girl (of whom she would've been her twin). Black Jack took pity on her as she wanted to live at all costs, and finally made her a doll-like body.
The A.I.M BURST from To Aru Kagaku no Railgun. It is the collective sorrow and despairs from the low-level Espers that used the Level Upper. Although it's not a human born fetus, it certainly qualifies for the terrible part. It's also the first arc's Final Boss.
In Chapter 49 of Hyde And Closer , we get a story about five people trapped in a tunnel: A business man,a wealthy couple,a policeman and a pregnant lady. The story basically tells how each one of them die one after another because of some creepy accidents. The catch is during the time they are trapped in the tunnel, the policeman was giving reports about how many people were still alive. He always gave the right number, but he always forgot to count one of them, the unborn child. The unborn baby was so furious for not being counted that he created those accidents to kill the people that were excluding him. In the end, he crushed his own mother under a rock and still managed to survive. Ouch.
The Watahiko in Mushishi. They're a fungus-like type of mushi that infect a pregnant woman, kill her developing child, and take on its form. If that's not enough, they multiply and have a Hive Mind.
Jinchuuriki in Naruto are often this, or at least regarded as such.
Arguably, Miaka's unborn child in the 3rd Fushigi Yuugi OVA counts as this, as it leads Mayo to the fake Suzaku. Subverted, however, because the rest is all Mayo's doing... and eventually allows her and Miaka to summon the real Suzaku.
Donna's friend and fellow Titan Raven is one of these, which is why her mom was spirited away to Azarath and allowed limited at best contact with her daughter. How well Raven can resist her "daddy's girl" tendencies determines which side of the Heel Face Revolving Door she's stuck on for a story arc.
The worst would have to be Ms. Marvel in The Avengers, who got spontaneously pregnant, went through hyper-accelerated gestation, and gave birth to a child who rapidly grew into an adult and mind-controlled her into being his lover. Not only is it squicky almost beyond description, it's nigh-unfathomable how this got past, well, anyone in a Comics Code approved book in 1980.
The same thing happened to Power Girl during Zero Hour; just replace "rape" with "incest", as the father was revealed to be her grandfather, Arion (in Post Crisis continuity). The baby grew up to become Equinox, who promptly defeated Scarabus, disappeared, and was never seen nor mentioned again.
One Big Bad of X-Factor was Haven, who sought to bring about the foretold apocalypse today instead of waiting for it to happen on its own after still more centuries of human suffering. She was led to do it by visions sent to her by "him," but never elaborates upon just who "he" is, though you figure she's talking about God. She's not: she's pregnant, and "he" is her unborn child and the true source of her power.
One of the main characters in Lucifer was impregnated by a pack of cards. With twins. One of which she managed to kill while it was technically unborn, the other took her hostage until she negotiated with it.
Cassandra Nova, the parasiting twin sister of Professor Xavier was one of these. In fact, Professor X's very first act of super heroing with his Psychic Powers was to fight her while they were both in the womb. It turns out she was an astral parasite (known as a Mummudrai) who was Xavier's opposite: Every bit evil as Xavier would be good. She's since become one of the X-Men's top villains.
One of the most horrible stories in Hack Slash had the slasher turn out to be a stunted murderous foetus who emerged from his obese adult twin brother's belly through a slit camouflaged between two rolls of fat.
A very short story in the same series had a fetus carve its way out of its laboring mother with a knife, kill the attending doctor, and attempt to crawl into Cassie Hack while she was waiting for a gynecological exam. Hack promptly squashes it, but still... where did it get the knife???
In Fables, Snow White gets pregnant by the Big Bad Wolf and gives birth to six babies. What she doesn't know at first is that she actually had seven babies. The seventh child was a invisible being made of wind and wound up killing some people to feed itself. Things got better after that, though.
The end of Bio Apocalypse involves an epic showdown between a 50 mile high fetus and a space fleet armed with nuclear weapons. Really.
Alien, obviously. There's a reason why the newlyborn is called a chestburster. It's made all the more horrible in Alien³, when Ripley is impregnated and you know she will die, one way or another...
A less apocalyptic but no less creepy version can be found in the Dawn Of The Dead 2004 remake, where a woman is bitten while pregnant and succumbs to the zombie plague. Her baby turns into a zombie fetus and is later born in a very gory scene.
Barbara Eden did a film called The Stranger Within, where she plays a woman who's taken over by the alien fetus she's carrying. In the end it turns out several women were impregnated, and they all get whisked off into space by the babies' father(s).
In Constantine, the plot revolves around a still unborn son-of-lucifer who should prove to be many times worse than the father.
A particularly creepy example happens in Ju On: The Grudge 2. The protagonist, Kyoko, is pregnant at the beginning of the film, only to lose her unborn child in a car crash caused by Toshio. However, later in the film, after a visit to the hospital, she discovers that her baby is somehow still alive. How can this be? All is revealed at the end of the film, when she gives birth to some dreadful, unseen thing, the sight of which causes all the present doctors to go insane and die horribly, while it shrieks inhumanly. Shortly after the adult spirit of Kayako crawls out of her womb, and, when Kyoko awakens from passing out, she sees her baby on the floor, tightly wrapped in a bloodstained piece of plastic. The finale of the film subsequently reveals that the child is Kayako reborn (or a child simply possessed by Kayako, depending on which fan theory you believe).
The direct-to-DVD movie Born revolves around this trope, where the pregnant protagonist's demon fetus causes her to kill people so that she can give birth. Then when the baby is born (looking just like a human baby even though her ultrasounds show it as a gremlin-like creature), she's told that she has a chance of saving it- when it's said throughout the movie that its birth would bring hell on Earth. The moral of the story: do not watch this movie.
The movie Grace is about one of these. A mother survives a car crash, but her fetal daughter is killed — but she insists on carrying to term. She does, and the baby is born seemingly alive. Only she bruises in sunlight, and has a thirst for blood...
A Nightmare on Elm Street 5: The Dream Child has Freddy trying to turn the main character's unborn son into one of these, feeding the fetus souls to strengthen it, presumably intending to either make the baby into his agent, or possess it. In a nightmarish flashback to Freddy's own birth, he's also depicted as one of these.
It's Alive. The first thing the baby does when its born is slaughter the attending medical staff. And in the sequels, the creatures get even more horrific...
In The Astronaut's Wife, Jillian becomes pregnant after her husband returns home from a questionable space expedition, and it's suggested that the fetus isn't entirely human. At the end, we learn that she had Creepy Twins, and they're possessed by aliens, as is she, after the being inhabiting her husband's body transferred into her when she killed him.
Prometheus picks up this trope from the previous Alien films and has a ball with it: Elizabeth Shaw recognizes right off that her pregnancy is abnormal, since she can't have children in the first place. Plus, it's grown far too quickly in the available time to possibly be human. Then she learns exactly what's growing inside her and immediately performs a Cesarean section on herself without adequate anesthetic, she's that desperate to get it out of her. The resulting baby/squid/facehugger hybrid proceeds to face-rape the Engineer, and begin a very familiar cycle.
A 1991 movie called The Unborn was all about this. It was about a couple who had fertility problems for a long time. They eventually undergo an experimental in-vitro fertilization procedure in order to successfully have a child. At first, they're ecstatic to be pregnant. Unfortunately, the doctor who performed the procedure was experimenting on the infertile women to produce creepily-intelligent, genetically modified babies. It was advertised as a horror film, but it was mostly depressing.
Damien Thorn Jr in Omen IV: Armageddon 2000. The pregnancy caused his mother terrible suffering and she died giving rectal birth.
Isaac Bashevis Singer's short story, The Black Wedding is about a Rabbi's daughter who is married to a demon and is eventually killed from the inside by her fetus. This story has a Cuckoos Nest twist though, as it is possible to read the character as being crazy and only hallucinating that her boisterous husband and his community are demons, and her ultimate death is merely from normal complications.
Mordred Deschain in The Dark Tower—while in the womb he forces his mother to eat frogs. He also has four parents, two of whom are human (and two of the main heroes). The other two are the Big Bad and the gender-bending incorporeal sex demon who raped the aforementioned humans at various points in the story.
The Christopher Pike novel The Grave was about a young woman who is impregnated by one of The Undead and killed by being dumped in a freezer. She becomes one of the undead herself and it is revealed that the fetus she is carrying was specifically bred by a Mad Scientist to become the antichrist. But by the end it's revealed the Mad Scientist has failed, the Fetus Terrible being more a balance between good and evil who destroys the Mad Scientist and goes on his merry way. Oh, and this book was aimed at teenagers. Really.
See also The Cold One.
Damon Knight's short story Special Delivery features a couple discovering that their unborn child is a hyper-intelligent telepathic bastard (in the magnificent, not biological sense), but when he's born the abrupt change in atmosphere turns him into an ordinary infant.
In Milton's Paradise Lost, the personification of Death is the child of the angel Sin and her father Satan. Her giving birth to him was so painful that it caused her to cry out "death", with the scream reverberating across the universe, and creating a child with the ability to destroy anything except for God. He subsequently raped her, resulting in a group of demonic dogs inhabiting her womb, causing her to exist in eternal agony. It's a weird, weird poem.
David Shobin's The Unborn. A pregnant woman takes part in an experiment where she's hooked to a super-computer. The fetus begins communicating with the computer and controlling the mother through hormones. Much horror ensues, including a failed abortion attempt, and worries about the baby being some sort of monster when born. At the end the baby is born, and is perfectly normal, hence a subversion.
Renesmee of Twilight bears all signs of being this, seeing as she feeds only on human blood and shatters her mother's ribs, pelvis and spine - but once she's born (by gruesome vampire-tooth C-section), she ends up a shockingly well-adjusted Creepy Child.
Glen Cook's Dread Empire books have the Unborn, a creature created by Varthlokkur from the (yes, unborn) fetus of a pregnant woman who was murdered. Played with in that while the thing is immensely creepy to everyone around it, it's not really evil and is actually essential as one of the few beings capable of reliably using magic when all magical energy starts becoming unreliable.
In Richelle Mead's Dark Swan series, it is prophesised that the first born child of the protagonist, Eugenie Markham, will bring about the end of the human world.
To avoid horrible spoilers, let's just say that this trope plays a plot-critical role in Tad Williams' Otherland as the origin story of one of the major characters.
A Song of Ice and Fire has Melisandre and her shadow assassins. Every so often, she'll lie with Stannis Baratheon, who she believes to be her religion's Messiah come again; when one of Stannis's enemies needs to be killed, she'll get in close and give birth to something made of shadow that can cut through steel and bone like paper ( as his brother Renly found out).
Mirri Maz Duurr believed that Daenerys Targaryen's child with Khal Drogo was this. So she did something about it. According to the possibly-exaggerated tales of the other women present, the stillbirth was hideously deformed, with scales and bat-wings, though it's not clear whether it was like this before or after Mirri performed her magic.
The novel Parasite Eve ends with the psychoactive child destroying everything around it as it goes through its birth phase before it is inevitably killed by male zygotes, meaning sperm hurts it.
The titular monstrosities of the short story Eumenides in the Fourth Floor Lavatory don't appear in an unborn state, but they look an awful lot like stillborn fetuses (with a fair amount of demon mixed in.) The term used for them is significant: "Eumenides" are otherwise known as "Furies," and these freaks are the main character's punishment for Parental Incest.
Particularly powerful psychics in Julian May's Mileu setting often develop powers and consciousness in utero. Fury, the Big Bad of the series used his Coercive powers to corrupt several of the Remillard dynasty's children before they were born. Later on the Well-Intentioned Extremist Marc Remillard's plan to boost human evolution would come unstuck when Fury's servants infiltrated the clinic where hundreds of unborn fetuses were being given metapsychic training and corrupted them all.
Subverted in the case of Jon Remillard. Sentient, aware, and superbly powerful from the first trimester, destined by genetics to become something thouroughly inhuman, he is the closest thing to a Big Good the series has.
In Dean Koontz's short story We Three, two brothers and sister, gifted with immensely far-reaching psionic powers, kill the entire human race. After that they beget a baby via Brother-Sister Incest - and the baby, still in utero, proves to be stronger that they three combined. And there's a strong possibility that the baby is a hermaphrodite, so it won't need the three protagonists after birth...
Who can forget the child/avatar of Proteus 4 in Demon Seed.?
In K.A. Applegate's Remnants series, there is "The Baby," born during the 500 year space flight, and controlling its mother Tamara through a psychic connection until she becomes a mere husk of her former self.
Used twice in Tencendor metaseries. The first, nearing fullterm, Gorgrael eats his way out of his mother in the prologue, and in the third novel his nephew, Dragonstar Sunsoar, orchestrate's his elder brother's kidnapping by Gorgrael from within the womb.
Jean-Baptiste Grenouille, the protagonist of Perfume: The Story of a Murderer, whose mother, as all characters who encountered him, died shortly after giving birth. Admittedly, she thought he was still born and decided to just throw him away with the debris of cleaning fish but Grenouille emitted a piercing cry and his mother was tried and executed for attempted child murder.
Ben Lovatt from Doris Lessing's The fifth child. Hariett Lovatt and her husband have a really great family of six, but Harriets fifth pregnancy is a nightmare - she feels like the fetus tears her apart from inside and is consumed with pain and exhaustion. Ben, when born, is a most unusual and frightening kid whose presence ruins the family.
And before he got his new body, he took the form of a small, monkey-sized humanoid that resembled a fetus (Rowling has mentioned that this is the bit she's most surprised got past the editors).
Brought up and explicitly feared in Tales of Kolmar. A dragon was turned into a human and married another human, which was prophesied to result in monster children and later a world brimming with demon fire with nothing to stop it. When Lanen got pregnant this pregnancy almost killed her several times, since the mingling of such different kinds of blood was hard on her body, but ultimately the trope was subverted.
In Waging Good by Robert Reed, the Earth's atmosphere is full of a variety of deadly nanomachines and tailored viruses after losing a war with its former colonies on the Moon and beyond. One type of artificial virus targets unborn children - mutating them into hellish abominations, like hiding poison factories in their stomach - or bladed monsters which try kill anything they see as soon as they are born. Because of this, Earth has "Jurors", people who test any newborn children as soon as they pop out. If they appear subverted, the Juror crushes their head against the nearest wall or table.
Live Action TV
Cordelia of Angel became pregnant and possessed with a Fetus Terrible. Twice.
If you count the "eye-in-the-back-of-the-head" thing, three times. It was even Lampshaded.
Also played with in the pregnant Darla storyline. It was written for a few eps as though she was pregnant with something terrible, although it was ultimately subverted.
So did Phoebe on Charmed, with Cole's child (conceived while he was posessed by the Source, and was thus destined to become the ruler of the underworld if born). Ultimately, the fetus was magically transferred to the Seer, who, unable to handle the sheer power it had come to develop, exploded violently enough to take down the entire Infernal Council with her.
Only Fools And Horses parodied this with the birth of Del Boy's son, Damien. When Rodney discovers the name to be given to the child, he is tortured by fantasies and nightmares that the as-yet-unborn child will grow up to be an evil, manipulative anti-christ. Of course the boy is nothing of the sort, but this doesn't stop Rodney from reading far too heavily into the small child's rebellious antics.
And there it was this Colombian Soap Opera titled "Me Llaman Lolita", where the heroine fell in love with the male protagonist since she was in her mother's womb, and her feelings radiated to her mother, leading to a series of tragic situations. Granted, she's not evil, but the whole premise is squicky as hell.
Let us not forget the long, drawn-out story arc on Xena: Warrior Princess in which Gabrielle is impregnated by the demonic god Dahak.
When Gail is pregnant with Lucas Buck's child in American Gothic, she sees the baby as this during her ultrasound.
Torchwood has an episode where Gwen gets her Face Full of Alien Wing-Wong at her Hen Do (Bachelorette Party) and she is tracked by the genetic mother of the fetus who wants to rip Gwen apart to get her baby. The Fetus Terrible element predominantly comes from Gwen and Rhys's parents thinking she's gonna have their grandkid juxtapositioned with Torchwood trying to figure out how to kill the fetus.
LOST's Aaron may grow into something terrible, depending on who you ask about the woman raising him.
Another example is in a flashback when Lois is pregnant with Reese and he kicks so hard that it's clear that he already has a nasty violent streak.
Subverted in that episode in Star Trek: The Next Generation, in which Deanna Troi becomes mysteriously pregnant, which makes some people very nervous, but it's really just a friendly alien wanting to learn about humans by incarnating as one for a short time.
One episode of Regenesis involves a baby specifically bioengineered by terrorists as a purpose-built carrier of a deadly, contagious hybridized plague, and implanted into the fetus of an unsuspecting mother in an attempt to bring about The End of the World as We Know It.
Ghost Whisperer's Melinda is pregnant and the Other Side has told her that her son will have even more powers then her, which will presumably draw unsavory spirits to them.
Isabelle Tyler of The 4400, while in her mother's womb, managed to injure Jordan Collier in such a way that healer Shawn Farrell was never able to completely repair.
The X-Files episode "Terms of Endearment" is all about a demon who's trying to father a child that isn't this. He just wants a normal human baby, and marries women and then kills them when they inevitably give birth to demon babies. (He kills the babies, too.) Unfortunately for him, he eventually marries a woman who wants a Fetus Terrible.
Riget: In the haunted Danish hospital, Dr. Judith Petersen's fetus develops much, much, much too fast. The mysterious father has disappeared, and her new boyfriend tries to convinces her to abort the F. T.. However, the child gets born towards the end of the first season, just when they try to carry out the abortion, and we follow its trials and tribulations throughout the second season.
In season 9 of Stargate SG-1, the Ori impregnate Vala with the Orici, basically their version of the Antichrist. As Vala herself put it:
Vala: Let's get something clear. She's not my daughter, Daniel. The Ori impregnated me against my will and forced me to bring her into the galaxy. I was an incubator. A shipping crate. And nothing more.
Zigzagged in the original V franchise, as Robin's pregnancy by a Visitor at first looks like this trope, causing her to crave raw meat and nearly killing her when an abortion is attempted. She gives birth to twins: a daughter who looks human, then reveals a reptilian tongue and poison spit, but grows up to be one of the good guys; and a short-lived scaled son who's the carrier of a toxin that becomes the heroes' chief weapon against the alien invaders. So he's a Fetus Terrible for humans in looks and for the aliens in physiology.
The creation myth in some American Indian cultures features the Good Twin and the Evil Twin. The Evil Twin is evil from the womb, and typically kills his mother trying to get born too quickly. He goes on to create death, disease and the Rocky Mountains*
My Cage: In this strip during Violet's ultrasound the doctor is quite terrified that the baby's heartbeat sounds like the theme from Jaws, but since this is Violet and Rex'sbaby, they seem quite pleased.
As a specifically non-human example, many species of sharks that give live birth have this as regular behavior in the womb. The litter of shark pups starts out more numerous, but the pups predate and eat one another until only the survivors end up being born.
Many shark species have two uteri, so will have two surviving pups. Call this an aversion if you will.
Ye olde ever relevant Dungeons & Dragons calls these little nasties "Unholy Scions" in the supplement "Heroes of Horror", giving the fetus a +6 intelligence bonus while still in the womb (the rough equivalence of taking an animal and making it a slightly stupid person, or of taking an average person, and making them a genius). Comes with a no-save allowed charm effect on the mother.
The Atropal is a DnD monster which looks like a giant fetus. It's technically supposed to be a stillborn god, though, and is undead, floating around outside of a womb, and in the 3rd Edition was technically unkillable due to a rules loophole. (It returns, even more horrible, in 4th Edition.) If killed, some of its chunks had a chance to eventually come back again as an Atropal Scion.
4e Atropal isn't a giant undead fetus anymore. This makes it way, way less creepy.
Werewolf: The Forsaken has the unihar, or "ghost children," which are created when two werewolves have a sexual relationship and the female gets pregnant. At birth, a twisted malformed spirit emerges and flees into the Shadow Realm, waiting to grow more powerful and exact revenge upon its parents.
In the predecessor, Werewolf The Apocalypse, most werecreatures are forbidden from mating with each other since the offspring will be deformed from inbreeding, and are commonly known as Metis. As Metis are born in war form and don't gain the ability to shapeshift until they're about 3 years old, their birth usually kills the mother. But while werewolf Metis are simply Wangsty outcasts, the werelizard variety are always stillborn and become evil, twisted spirits.
Changeling The Lost has Fetchspawn, the offspring of a Faerie human-impersonator and a human they've fallen in love with; they're generally born sociopathic monsters who are very likely to disappear into the Hedge one day, but that doesn't mean that's where the trouble starts. The extremely rare occasion that two Changelings actually manage to reproduce may also spawn a child as half-fae as their parents, whose Fae nature can be detectable (or even obvious) before its birth.
Mage The Ascension had the Widderslaint in the Book of Madness, reincarnated Nephandi (mages who are evil because of their warped souls— or possibly whose souls are warped because they're evil). The fluff text describes a Widderslaint infant who crawled into his twin brother's crib and strangled him to death.
FATAL has a particularly depraved version in which people can be made pregnant by a rapist sword and give birth to another sword. And this, friends, is why you Should Not Play FATAL.
In Silent Hill 3, it turns out that Heather is "pregnant" with a freakish God (or devil, whichever you like.) Made more terrible when she vomits up quivering God-fetus. Made more more terrible when Claudia eats it.
The first Parasite Eve becomes a race to stop this in the game's latter half. In a strange twist, the pregnant "woman" in question is doing this deliberately.
Shin Megami Tensei III Nocturne has as one of the three last major enemies Noah, God of Solitude. Isamu as the core, curled up in a fetal position surrounded by a red orb Equal parts this trope, Body Horror and pure terror.
In Persona 4, you have Shadow Mitsuo, though it's usually hiding inside a giant 8-Bit warrior.
In the massive Dragon Quest romhack Dragoon X Omega, the Big Bad is revealed to be a goddess, corrupted by her unborn child. After the first round, it tears from her womb to continue the fight.
In Haunting Ground, Riccardo needs Fiona's womb/azoth so she can give birth to him (possibly repeatedly) as a means of living forever.
Fate/stay night has this, when Sakura is (sort of) the mother of Angra Manyu, the world's evil in physical form.
In actuality though, Angra Manyu is just a poor nameless Persian man who his village sacrifice just so they can have some peace of mind.
At the end of FEAR 2, Alma "rapes" Beckett and gets pregnant.
Then Alma puts Beckett's hand to her stomach and a little voice, which is not Alma's, says something like "daddy" or the like.
At the end of Overlord: Raising Hell, it is shown that the Overlord's mistress is pregnant. Said hellspawn is the protagonist of Overlord II.
In Final Fantasy VII, Lucrecia Crescent allowed her unborn child to be injected with Jenova cells. The direct result of this experiment was the main antagonist Sephiroth. During her pregnancy, Lucrecia got horrible pain attacks and visions of what her son would become. Granted, it was actually the Jenova cells causing the illness and visions, not the fetus itself, but still.
Played with in Earthbound with Giygas, the final boss. Giygas' final form resembles a sea of screaming faces forming the outline of a fetus.
There is an infamous theory that Giygas is one and that at the end of the game, you travel back in time to kill it at its weakest state when it was a fetus.
The Nihilanth from Half-Life resembles a giant fetus (with a third arm growing out of it's chest and a head that opens up).
Dr. Fetus is probably the most actively evil fetus ever, and he does it all in his mechanical, tuxedo and monocle wearing preservative jar. Can possibly be an Enfant Terrible since he's out of the womb, but he's also still a fetus.
Dragon Age: Origins may in fact have the ultimate Fetus Terrible from Hell! When an archdemon is killed, the Old God that inhabits it will simply jump into the next tainted creature nearby. The only thing to prevent that is to have a Grey Warden deal the killing blow as they gain their powers from the taint, but still have their own souls, so the soul of the Warden and the Old God will annihilate each other. Flemeth has come with a magic ritual that enables her daughter Morrigan to become pregnant with the child of a Grey Warden and when a Gray Warden deals the killing blow to the archdemon, the Old Gods spirit will jump into the tainted child. Since the fight against the archdemon is only a few days after the ritual, the child does not yet have a soul and will become the Old Gods new body. Morrigans only condition for going through with it is and saving the Grey Wardens to sacrifice themselves, is that she is to keep the child herself to raise it.
Even made more horrifying by the fact that Flemeth has gained virtual immortality by merging her own soul with a lesser demon while still stying herself, and stealing her daughters bodies when her own becomes too old. If Morrigan had never found out about it, Flemeths plan was apparently to take over the demon child to merge herself with an Old God, making her the most powerful being that ever existed, surpassed only by the Maker himself.
However, Morrigan does mention that the child will be born free of the taint and that it will be cared for. There's a lot of predictions in Wild Mass Guessing that the child will be a protagonist in a future Dragon Age game in which case it would be up to the player to decide if the Old God Baby All Grown Up is a true Fetus Terrible in the making.
In Dead Space, there are the Lurkers. Originally, they were clone-fetuses being grown in People Jars as spare body parts for the miners aboard the Ishimura, but became necromorphs. They crawl up the walls and shoot slime at you from their Combat Tentacles.
In Batman Arkham City, if you search Joker and Harley's HQ, you can find a positive pregnancy test laying around indicating that Harley is pregnant with The Joker's child. The fact that the child was conceived while The Joker was suffering the side-effects of Titan can lead to some pretty terrifying implications.
Comes up again in the closing credits if you listen long enough.
"Hush little baby / Don't say a word / Momma's gonna burn down / The whole damn world..."
However, it's heavily hinted in Harley Quinn's Revenge that Harley merely got a false positive on her test after a long string of negatives.
In The Binding of Isaac, If you beat the game 10 times, a boss called It Lives will replace Mom's Heart. It Lives is a giant fetus attached to Mom's Heart as a result of pregnancy Gone Horribly Wrong. The battle is no different from Mom's Heart aside from the fact that It Lives summons bosses during the battle. Not only that, but you face It Lives in your own mother's womb.
Dr Fetus also makes a cameo appearance as an upgrade which replaces your tears with bombs
In Cry Of Fear, one kind of enemy is a pale-skinned pregnant woman whose unborn child bursts out of her womb to attack you with knives. It can also mind control you into killing yourself unless you resist the influence.
Medivh from the Warcraft series. He was possessed by the spirit of Sargeras (Warcraft's equivalent of Satan) while he was still in his mother's womb. He got better by the time of the third installment.
The third Darkstalkers game has one, the Shintai, as a plot element - one of the titular Darkstalkers, Jedah, is hoping to use it to rewrite reality. It's shown in the background of the "Fetus of God" stage, and its disgusting, skinless look has been known to unsettle players.
In thisSluggy FreelanceB Side Comic, a demon baby kills its mother when it bursts out of her stomach and bites its father's head off three seconds later. This sort of mass carnage during child birth is apparently normal among demons.
In the Whateley Universe, there's a classic example in a Lovecraftian sense. A woman whose ancestry isn't all human is made pregnant by a demon whose parent is Shub-Niggurath. The unborn child is predicted to be a powerful demon whose progeny will wipe the earth clean of humans. The mother is killed. Subversion: the mother is killed over twenty years too late, and the child grows up apparently human until his death. At which point it comes back to life and fights like hell not to be turned into the predicted demon. Currently in this universe, said character is one of the heroes. So far.
Completely and utterly inverted in Metamor City with Darla, who is an abnormally intelligent with massively powerful telepathy and precognition. Despite this she is a completely innocent unborn child. She is so powerful enough that she could stun Victor when he was telepathically listening despite him having a partially cybernetic brain to protect his mind that protects against and fools other powerful telepaths. Unfortunately her death at the hands of her psychotic father is a Foregone Conclusion.
Parodied by Family Guy with Stewie's 'brother', Bertram, who was plotting to kill Lois as a sperm . Once he was born via sperm donation received by a lesbian couple, though, he seemed to focus more on a rivalry with Stewie.
Stewie himself. He planted a bomb in Lois' womb before he was born.
Stewie: Happy fiftieth birthday, Lois.
A particularly gory South Park episode, "Woodland Critter Christmas", had this with a pregnant porcupine, bringing a whole new meaning to Grotesque Cute.
When Kenny's mother is pregnant in "Cartman Joins NAMBLA", Kenny, who spends the episode trying to get rid of it for whatever reason, has a nightmare about the child's inevitable birth where it turns out to be a demonic creature of some sort, killing him and everyone else in the hospital room.
In The Venture Brothers, we find out in the first season finale that Dr. Venture himself was one. When his was in the womb, he ate his own brother, who later turned out to have survived inside his body for his entire life to come out as a baby that is missing an arm and has the head of a full-grown man.
In Frisky Dingo, Antagone, becomes pregnant and due to her exposure to radioactive waste and ants, her unborn child mutates into an enourmous mutant ant-baby. "Hero" of the show Xander Crews tries to stop the baby from being born. He fails (or rather, the man he sends to do it refuses to follow through), and the baby is born, eats Antagone and goes on a rampage.