How Does Mpreg Work Anyway?


A lot of people hear the word “mpreg” and they’re confused by it. What is it? While most people conclude it is a niche kink, mpreg is often more mainstream than we think. We can look to plenty of “mainstream” shows, like Fairly OddParents or Big Mouth, as well as movies like Junior or, perhaps most famously, Alien.

A sculpture of the xenomorph, the ferocious alien depicted in the Alien franchise, in a crouching position with its knees on the floor, feet tensed to spring, and tail extended.
Some people find these things scary; others … have a different reaction.

For the most part, these more mainstream incarnations tend to play the idea of mpreg off as either a sort of ha-ha funny thing or a horrifying possibility (see Alien). Yet, in most cases, they don’t really address how mpreg would work.

Which is sort of why people tend to be so confused about it when they come to the more “niche” works that are for enthusiasts. That kind of media treats mpreg less as a joke and more as a serious exploration. So, how the hell would that even work?

It Takes a Lot of Mucking with Biology

If we’re talking about how mpreg works, we can only make some generalizations. Every piece of media you encounter will do something a little bit different, so unless you look specifically at, say, The Left Hand of Darkness or a smutty omegaverse fanfic, “how” mpreg works can’t necessarily be explained.

In principle, though, mpreg functions on the idea that men can get pregnant. In most cases, people take this to mean cisgender men, as in those who have “male” biological coding, with a typical XY phenotype.

Real Life Scenarios

Generally speaking, mpreg ignores “real life” instances where biology would allow for mpreg. Perhaps the most common version of this is trans men. Trans men often have XX phenotypes, which means they have the right “equipment” to become pregnant and carry a child to term. There is really no intervention or magic or biological engineering that needs to go on to make this happen.

Intersex individuals may also represent a type of mpreg, in the sense that some intersex individuals identify as men. They may not have a stereotypical XY or XX presentation, and, indeed, they might present as men but have an underlying XX phenotype. Or they may have another condition that gives them characteristics of both the XY and XX phenotypes.

Most mpreg does not focus on these sorts of cases. They’re most interested in case of stereotypical XY phenotype humans becoming pregnant, which is something of a biological impossibility.

So, how does mpreg work then?

Usually, it involves some sort of biological fuckery, if you will. Omegaverse is a very clear example. In the omegaverse, “male omegas” who can become pregnant exhibit XX phenotypical traits. They may also exhibit XY phenotypical traits, but the XX traits allow them to become pregnant and carry a child to term.

Very few authors really wrangle with what that actually means—most “male omegas” in omegaverse stories are actually intersex or, perhaps, trans men.

The Horror Scenario

In something like Alien, we have the horror scenario. That’s simply a cis guy being impregnated, usually against his will. This is treated as horrifying, and the offspring is usually treated as a parasite. In the end, he usually dies or is crippled. The chest-burster in Alien is a perfect example of this.

In this case, we’re not really interested in “how” mpreg would work. The point is more that pregnancy—especially forced pregnancy—is a dangerous, even terrifying, condition for many people.

Biological Engineering or Virus

In some cases, stories will take a sort of “sci-fi” stance on mpreg. These stories tend to focus on mpreg as the result of science and technology. In some cases, mpreg has been biologically engineered. Usually, we’re looking at a sort of dystopian future world, where the need for cis men to become pregnant has become apparent.

Some scientists have speculated that mpreg would be possible in our real world. The question is how safe it would be for a cis guy and the offspring to undergo this. At the current time, most feel it would be completely unethical to do more than conjecture about how mpreg might happen.
In some stories, mpreg may happen as the result of intentional gene editing. In other stories, it may happen as the result of womb transplants, drugs, or other “body modifications.” And in other scenarios, the mpreg possibility comes about because of something more sinister—such as a virus or parasite that rewrites DNA.

None of these scenarios are actually that far-fetched. We know there are parasites that effectually hijack male crabs and turn them into female crabs. Nature is crazy, so even if these scenarios seems implausible, they’re certainly not impossible.

The Technological Advancement

Another answer to “how does mpreg work?” Is that there is a technological advancement. This is sort of The Left Hand of Darkness solution. In this novel, Le Guin paints a society that has created artificial wombs outside the body. The result is that no one has to carry a child inside their own body and anyone can become pregnant—“male” or “female” notwithstanding.

An image that shows a number of humanoid infants in rows of incubators, depicting an "artificial womb" facility, which was revealed to be a hoax.
This was revealed to be a hoax, but the idea exists.

Again, this scenario isn’t entirely far-fetched. We have made technological advancements that allow conception to happen outside the body, and we have also made advancements that allow infants born extremely prematurely to survive outside the womb. (At the time of writing, the current survivability threshold is around 22 weeks, almost half the pregnancy, although the infant’s odds are not good and premature babies usually suffer lifelong effects.)

And there is speculation that we will soon have artificial wombs to take the “Petri dish” conception and implant there, rather than a person’s body. While this is further off than some would have you believe, it’s, again, not outside the realm of possibility.

The More Fantastical Route

Some authors prefer to go with more “fantastical” explanations for their mpreg. A typical answer here might be that “a wizard did it.”

And that is sometimes the answer to “how does mpreg work?” Sometimes, mpreg is the result of a curse or a magic spell.

More commonly, it’s the result of the biology of a fantasy species. This often combines the more scientific route with the “fantastical route.” Aliens, werewolves, and vampires—among others—have no real reason to cleave to human notions of biology. Heck, a lot of nature doesn’t do that—just look at seahorses and pipefish. Mpreg is par for the course in those species. In slugs and worms, individuals are often simultaneously hermaphrodites, meaning they can be both “male” and “female” at once. And some species change sexes as part of the natural life cycle, such as clown fish.

A yellow seahorse faces the left of the frame, while a baby seahorse emerges from its pouch.
A baby seahorse emerges from its father’s pouch.

So, why would an alien or a vampire or anything else necessarily conform to “human” standards? The sky’s the limit when we start dealing in legend and imagination.

Of course, we can also then toss considerations about gender into the mix. Do crabs have gender identities? Well, we don’t know. Do clown fish? If a clown fish changes sexes, does it shift from being “a boy fish” to being a “girl fish”? Or does it have a stable sense of identity? We don’t even know if fish have a sense of identity, so we really have no answer to this one.

And from there, it’s easy to speculate that, even if fish did have a sense of identity, their conception of gender might not line up with human conceptions of gender.

The Nitty Gritty Mechanics

Okay, so we’ve looked at the big picture, high-level ideas of how mpreg might work in any given world. So now we circle back to the question: how does mpreg actually work in any of these scenarios?

Again, we have to leave it to individual authors to work out the exact mechanics in their own stories, scenarios, and worlds. No two worlds will function alike; indeed, even stories may differ within the same universe or series.

All that said, we can make a few generalizations about how mpreg works.

First, as I said, it usually involves a (cis) man becoming impregnated. This means the man has to have some kind of apparatus that allows him to get pregnant and carry a child.

The next question people usually have is how the man gets impregnated. For the most part, this usually means he’s inseminated by another guy.

This can happen in a few different ways. Sometimes it’s a Petri dish sort of thing. Sometimes it’s alien biology, such as Kiff in Futurama, where he becomes impregnated by holding hands (whoops).

In a lot of cases, though—and especially if we’re dealing with smutty fanfic—there’s a very simple answer. It’s buttsex.

Now, some authors will play with that, especially when we run up against worldbuilding like omegaverse. The author may specify that “omega” is a secondary sex, and some omegas will present more like intersex individuals. Some will be full-on hermaphrodites (in the biological sense). And in other cases, the author says, “Nah, there’s only one hole.”

Sometimes, authors don’t really specify this, so you’re on your own. In effect, it’s up to you to determine what you think is happening—is this a cis guy having anal sex, or is there some biological witchery going on here?

Where Does the Baby Come Out?

This is probably The Question in mpreg. A lot of writers lampshade it—especially when the story treats mpreg as a unique case or a one-off (such as when “a wizard did it”). They’ll have their characters ask this question, usually accompanied by a good dose of freaking out while asking it.
Nobody usually likes the answer. Most of the time, the answer is the same as it is in real life: the baby comes out the same way it went in.

For cisgender male characters, this leads to “ass babies”: they had anal sex, and the baby is delivered via the same route.

If we’re dealing with a world where mpreg is more common, such as in an omegaverse story or a world with trans men or intersex individuals, the answer may be the same, but it’s treated as being a little more normative or acceptable.

Very rarely do characters give birth via the penis, although some authors definitely do choose this route. Sometimes, the mpreg penis birth is played for laughs. It can also be treated as the more horrific route.

Some authors opt to have their characters give birth via C-section. Depending on the world, this might be the norm for mpreg scenarios, or it may be chosen because of the uniqueness of the situation. It really depends on the writer and the world they’ve built.

Eggpreg usually results in someone laying an egg. This can go either way as well.

Some authors skip right over birth scenarios, while others prefer to include long, drawn-out scenes. As a reader, you have plenty of options. If you’d rather not know the nitty-gritty details, there are stories that will hop right to the part where everybody gets to snuggle with a cute baby.

Summing Up: How Does Mpreg Work?

The basic answer here is mpreg works any way you—or the author—want it to. There’s no shortage of scenarios that lead to or support mpreg, from real-life situations to more fantastical explanations, like alien biology or a wizard did it. Different authors will choose different worldbuilding mechanisms to incorporate mpreg in their worlds—and those different mechanisms can lead to different mechanics behind how mpreg itself works.

About the author

By Cherry

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