Using the D&D 5e RPG system. We'll use a Brown Bear and the spell Banishment as an example. What, if anything, occurs when you attempt to cast such a spell on a creature that is currently pregnant?

The spell specifies the following:

You attempt to send one creature that you can see within range to
another plane of existence. The target must succeed on a Charisma
saving throw or be banished. If the target is native to the plane of
existence you’re on, you banish the target to a harmless demiplane.
While there, the target is incapacitated

Does the spell take effect and if so does it bring the as yet unborn creature(s) with the mother? Possible complications include, beyond the spell only targeting a single creature, that it must also be a creature that you can see. The supposition is that being inside another creature would provide those inside with Total Cover.

A target with total cover can't be targeted directly by an attack or a
spell, although some spells can reach such a target by including it in
an area of effect. A target has total cover if it is completely
concealed by an obstacle

This kind of situation is up to the DM.

D&D 5E isn't designed to handle these sort of situations. The system doesn't have any built-in mechanics for pregnancy, or whether pregnant creatures can be individually targeted by spells. The system simply doesn't have the rules to address it. So by Rule Zero, the DM should make the call.

Note that the DM should be really careful about approaching these topics, as they tend to be sensitive and controversial. Even if players overlook the ethics regarding a pregnant dragon or monstrosity, this could set an unpleasant precedent for similar scenarios with humanoid creatures.

The DM's decision should respect the table's social contract. Some players may accept the grotesque horror style you're considering, whereas others may consider it seriously offensive. And making the players uncomfortable generally results in a poor gameplay experience.

Let's set pregnancy aside for a moment and consider some other aspects of this issue.

If you have harmful microbes in your body, does this spell leave them behind? If so, then it's effectively a Cure Disease for anything caused by foreign pathogens. That's the good news, but...

Every human body contains a host of symbiotic bacteria that help us with digestion and fighting off pathogens. Does banishment leave these behind? If so, anybody affected by this spell is likely to get very sick if not die from opportunistic infections and inability to digest.

Some RL creatures use symbiosis for other purposes. Green tree sloths have symbiotic algae living in their fur; the algae helps camouflage them and provides nutrition. If you banish a sloth, does it lose its green camouflage and suffer health effects from loss of nutrition?

Aside from the obvious issues of taste and player discomfort, applying a strict interpretation of "one creature" risks bogging your game down in endless argument about this sort of issue. Setting that precedent risks getting your game bogged down in interminable arguments (what exactly are the effects of losing your symbiotes? Do elves and dwarves have the same kind of symbiotes as humans?)

Now consider multi-headed fantasy monsters like ettins, hydras, and chimeras. In some cases their heads are capable of independent thought, even arguing with one another. But for D&D's purposes, a multi-headed monster is still considered a single creature. Otherwise, banishment would presumably kill all but one head. Given that a fetus has less autonomy than an ettin's second head, it seems consistent with existing practice to treat it as part of the parent.

(Note that teleportation effects generally take a generous interpretation of what counts as a single person - usually you get to keep your clothes and equipment.)

The mention of "a harmless demiplane" would seem to suggest that this spell was not intended to cause other kinds of harm - else presumably the spell description would mention it.

The pregnant creature and its unborn progeny remain together because as DMs, we strive to keep our games Humane

There are a number of questions that we would be forced to ask and resolve if we attempted to make a purely RAW interpretation of this question—questions I have no intention of resolving. These questions include

• Is the unborn child considered its own creature?


• Does the age of the unborn child matter?


• Do the intentions of the pregnant creature matter?


• Should the unborn child make its own Saving Throws?


• Do the intentions of the spellcaster matter?

So, ignoring all of those questions, we'll address the question: does the unborn progeny get banished the same as its parent, or remain behind the same as its parent, or not?

The answer, as far as I'm concerned, is yes, it does. Either they both get banished, or neither are banished, contingent on the results of the parent's Saving Throw.

You know why?

Because Dungeons and Dragons is a game, and games are about having fun. Dealing with the sociopolitical and metaphysical questions about conception and personhood, or reckoning with the biological consequences of an unborn child being forcibly and unnaturally separated from its parent are grotesque, and are things that will interfere with the capacity of the game you are playing to be fun.

Having said that...

If you as DM have affirmatively agreed with your players that you are willing to play in such a manner that all of those previously mentioned questions are open season and deserving of itemized responses AND that you and all of your players are comfortable dealing with the grotesque results of whatever rulings result, then you may make whatever ruling you deem fit, based on those criterion I mentioned previously and how you choose to answer them.

From a strictly physical sense, a pregnant creature is physically attached to its unborn progeny by an umbilical cord.

Unless your spell is going to sever that, they're a single contiguous entity and I'd expect to banish them together.

I'm not aware of any examples of banishing physically linked entities that would separate them!

The rules don't handle pregnancy so it's up to you.

Should I have pregnancy and fetus rules in my game?

As others have pointed out, this is something that gets very complicated and thus might be better to be left alone. The rules don't say explicitly how a fetus is to be handled. We need not get into the reasoning behind why it isn't handled, but why you have pregnancy rules might matter a lot to your setting and your players.

Whether or not you handle pregnant creatures as differently from other creatures has serious implications for your setting. When is a fetus alive? Do they have stat blocks? Can they be targeted? Is this the type of thing that NPCs regularly worry about? Is infanticide something you want in your setting? Think long and hard about that last one, because that is the can of worms you are opening up. I'll ask it again, because it's very important. Is infanticide something you want in your setting? Make sure your players are okay with that type of thing, but I think you ought to avoid surprising them with a fetus left behind after banishment. Is the shock value really worth darkening the tone?

Additionally, it might raise questions from your players you might want to avoid that could be distracting. Morality is something that can easily distract a group of players and often does. Arguments are fun but you might be biting off more than you can chew here. Be aware of the minefield that is the debate of whether or not a fetus is life. That is not to say that this should bar you from inviting that discussion to your table if that's what you want to do. Very often the characters in our setting have a very different set of morals than our players do. What is acceptable in one city might be taboo in another. One tribe might consider a fetus life, another might consider it not. Just like real life, huh?

Talk to your players first

Because of the implications behind this whole thing, you should ask your players if this is something they'd like to explore. It's your job as DM to ensure the party is having a good time, and while you may want to explore the darker, more complicated side of pregnancy and spells, your players might feel differently. You can already tell it's made many of us uncomfortable already. Imagine how your players feel. If they all agree that this would be the type of thing they want to deal with, then you need to decide how and why it's handled. Again, there are no rules for pregnancy.

Follow Roger Rabbit rules. ”Only when it is fun[ny]”.

The entire multiverse is there to serve the purpose of playing.

If the DM can see a usable story element in leaving behind an absolutely adorable baby bear who then thinks the party is Mom & Dad, and that will suit the party, then go for it.

Of course, you're loading Chekhov's Gun. Momma bear will be back...