Utero

The Utero is an alternate floor to the Womb. Unlike other alternate floors, the Utero does not need to be unlocked, aside from unlocking the Womb. While the theme of Utero overlaps heavily with the Womb, it appears to emphasize gore and disfigurement rather than its counterpart's focus on 'intact' viscera, though the difference in enemy make-up is still more subtle compared to other floors nonetheless. Its walls are slightly different, and the floor contains several new enemies that are bloodier and more deformed, as well as more enemies borrowed from later chapters, such as the Cathedral and Sheol.

Like the Womb, all damage that is taken on this floor and onwards deducts a full heart from the player's health (unless the player has The Wafer), regardless of the source. While in the Utero, a dark yellowish desaturated screen shader and a warping effect will be applied to the screen, making it appear as if the area is submerged in fluid and further distinguishing the floor's appearance from the Womb.

Monsters

Entity	ID	Description
Baby	38.0	Slowly floats towards Isaac and fires a blood shot at him. Occasionally teleports and reappears elsewhere.
Boil	30.0	Stationary enemy that decreases in size when hit, but regenerates to its full size until fully destroyed. Fires multiple short-ranged blood projectiles in random directions when fully swollen.
Walking Boil	88.0	Does not shrink or regenerate. Walks around aimlessly and fires multiple short-ranged blood projectiles in random directions.
Bony	227.0	Wanders around the room and throws a bone at Isaac when he is in sight.
Death's Head	212.0	Invulnerable enemy that moves diagonally around the room, dealing contact damage. Dies when the room is cleared.
Brain	32.0	Slowly crawls around the room, leaving a trail of Red Creep.
MemBrain	57.0	Slowly moves around the room, occasionally hopping and firing 8 large blood shots in all directions. Splits into 2 Brains upon death.
Clotty	15.0	Randomly wanders around the room, firing 4 blood shots in the cardinal directions.
Clot	15.1	Randomly wanders around the room, firing 4 tar shots in the ordinal directions.
I.Blob	15.2	Randomly wanders around the room, firing 8 shots in all directions.
Dip	217.0	Slowly dashes in random directions, dealing contact damage.
Squirt	220.0	Dashes towards Isaac and deals contact damage. Spawns 2 Dips upon death.
Dinga	223.0	Slowly moves around the room, occasionally hopping to spawn Dips or fire 8 Brown shots in all directions. Splits 2 Squirts upon death.
Dople	53.0	Mirrors Isaac's movements and fires blood shots at the same time as Isaac. Can be damaged by spikes.
Embryo	77.0	Aimlessly hops around the room, dealing contact damage.
Eye	60.0	Slowly turns towards Isaac and fires a Technology laser at Isaac if he stands still or is too slow.
Bloodshot Eye	60.1	Slowly turns towards Isaac and fires a Brimstone beam at Isaac if he stands still or is too slow.
Pale Fatty	208.1	Slowly walks towards Isaac. Occasionally farts and shoots 6 blood shots in all directions. Has a chance to turn into a Blubber upon death.
Fat Sack	209.0	Slowly walks towards Isaac. Occasionally leaps off-screen and attempts to land on Isaac, leaving a puddle of Red Creep and shooting 6 blood shots in all directions where it lands. Has a chance to turn into a Blubber upon death.
Blubber	210.0	Walks around aimlessly and randomly spews a cluster of blood shots in all directions. Has a chance to turn into a Half Sack when killed.
Half Sack	211.0	Wanders around aimlessly and leaves a trail of Red Creep.
Fly	13.0	Hovers in place. Does not deal contact damage and is harmless, but can turn into Pooters if they stay around Poop.
Eternal Fly	96.0	Invulnerable fly that circles Corny Poop and various monsters. Deals contact damage. Turns into a vulnerable Attack Fly after the object or monster it circles is destroyed.
Moter	80.0	Follows Isaac, similar to Attack Flies. Deals contact damage. Splits into 2 Attack Flies upon death.
Pooter	14.0	Slowly drifts toward Isaac, occasionally firing a single blood shot at him. Does not deal contact damage.
Super Pooter	14.1	Slowly drifts toward Isaac, occasionally firing two blood shots in a V-formation at him. Does not deal contact damage.
Full Fly	249.0	Flies toward Isaac erratically, dealing contact damage. Releases 6 bullets in all directions upon death.
Red Boom Fly	25.1	Flies across the room in straight diagonal lines, dealing contact damage. Creates a ring of 6 blood shots upon death.
Sucker	61.0	Flies slowly towards Isaac, exploding into 4 shots in the cardinal directions upon death.
Spit	61.1	Flies slowly towards Isaac, firing an Ipecac shot towards Isaac upon death.
Fred	59.0	Hops out of the ground and burrows elsewhere, firing 4 blood shots in the cardinal directions. Occasionally fires red Ipecac shots at Isaac.
Globin	24.0	Chases Isaac, dealing a full heart of contact damage. Upon taking enough damage, it collapses into a pile of goo, which can be killed. Will regenerate after a short period of time if not killed quickly.
Gazing Globin	24.1	Quickly chases Isaac, dealing a full heart of contact damage. Upon taking enough damage, it collapses into a pile of goo, which will slide away from Isaac and can be killed. Will regenerate after a short period of time if not killed quickly.
Grub	239.0	Erratically moves around the room like Larry Jr. and charges at Isaac when he gets within its line of sight. Spawns Maggots, Chargers, or Spitties upon death, one for each of its segments.
Gurgling	237.0	Charges towards Isaac when he lines up with them, leaving a trail of Red Creep and shooting 6 blood shots.
Guts	40.0	Attaches itself to a wall or obstacle and rolls around it.
Mama Guts	57.1	Slowly moves around the room, occasionally hopping and firing 8 large blood shots in all directions. Splits into 2 Guts upon death.
Homunculus	228.0	Starts attached to the wall or an obstacle. After a while, it detaches, shooting 6 blood shots in all directions, leaving a puddle of Red Creep and chasing Isaac. If it dies while still attached, it will still leave a puddle of Red Creep.
Leech	55.0	Quickly charges towards Isaac when he gets in its line of sight.
Holy Leech	55.2	Quickly charges towards Isaac when he gets in its line of sight. Explodes upon death. Spawns with an Eternal Fly circling it, which instantly dies when the Holy Leech explodes.
Lump	56.0	Fires 3 spread blood shots at Isaac when he gets in its line of sight. Will burrow underground and reappear elsewhere after firing.
Charger	23.0	Slowly moves around the room, charging at Isaac when he gets in its line of sight.
Mask + Heart	93.0	The Mask is invulnerable and moves around erratically, charging at Isaac when he lines up with it. The Heart avoids Isaac and fires 4 blood shots in the cardinal directions when Isaac gets near. Killing the Heart will automatically kill the Mask.
Knight	41.0	Moves erratically around the room and charges towards Isaac when in line of sight. Can only be damaged from behind.
Maw	26.0	Slowly floats towards Isaac, firing a blood shot at him when he is in their range.
Red Maw	26.1	Floats quickly towards Isaac and releases 4 blood shots in the cardinal directions upon death.
Psychic Maw	26.2	Slowly floats towards Isaac, firing homing shots at him when he is in their range. Spawns with an Eternal Fly orbiting around it.
Mr. Maw	35.0	Walks towards Isaac and attacks by launching its head towards him. Turns into a Maw or Gusher upon death depending on the killed body segment. Occasionally separates at will.
Mom's Hand	213.0	Falls from the ceiling. If it lands on Isaac, it deals damage and teleports him back to the spawn room of the floor. Entering a room containing Mom's Hand will warn Isaac with Mom's laugh.
Swinger	216.0	Slowly moves towards Isaac as its head swings around its base. Upon death, spawns a Maw or a Globin depending on which part is killed.
Nerve Ending	231.0	Static enemy which acts as a meat shield.
Oob	224.0	When Isaac lines up with it horizontally, it charges across the room once. When Isaac is not horizontal to it, it spawns Brains.
Para-Bite	58.0	Moves towards Isaac, dealing contact damage. Can burrow underground and reappear elsewhere.
Cod Worm	221.0	Stationary enemy that hides in a shell and spews a burst of blood shots if shot at. Only vulnerable when it pops its head out.
Red Host	27.1	Stationary enemy that can be damaged even when its head is lowered. Fire 5 spread blood shots when it raises its head.
Flesh Mobile Host	247.0	Acts like the Red Host, but follows Isaac and deals contact damage.
Rotty	226.1	Slowly walks towards Isaac, leaving short-lasting Red Creep behind itself. Spawns a Bony or two Attack Flies upon death.
Round Worm	244.0	Pops out of the ground in random locations and spits a blood shot at Isaac if he is in sight.
Spider	85.0	Erratically moves around the room. If Isaac gets close to it, it chases him, trying to deal contact damage.
Big Spider	94.0	Erratically moves around the room. If Isaac gets close to it, it chases him, trying to deal contact damage. Spawns two Spiders upon death.
Crazy Long Legs	207.0	Chases Isaac, dealing touch damage. Occasionally stops to spit 8 blood shots in all directions.
Small Crazy Long Legs	207.1	Chases Isaac, dealing touch damage. Occasionally stops to spit 4 blood shots in the diagonal directions.
Wall Creep	240.0	Crawls along walls to try to line up with Isaac and shoots three blood shots in a line.
Blind Creep	242.0	Randomly crawls along walls and shoots three spread blood shots.
Rage Creep	241.0	Slowly crawls along walls to try to line up with Isaac and shoots a Brimstone laser.
Tumor	229.0	Moves around the room diagonally, occasionally firing 6 blood shots in all directions. Fires more often upon getting damaged.
Vis	39.0	Randomly wanders around the room. Pauses to charge and fire a Brimstone laser when Isaac gets in its line of sight.
Double Vis	39.1	Randomly wanders around the room. Pauses to charge and fire a Brimstone laser which fires from both sides when Isaac gets in its line of sight.
Chubber	39.2	Randomly wanders around the room. Pauses to fire a Charger that deals one heart of damage when Isaac gets in its line of sight. The Charger is invulnerable, blocks Isaac's tears, has limited range, and flies back to the Chubber.
Wall Hugger	218.0	Moves around the room like Guts, damaging Isaac by contact. Cannot be destroyed.
Stone Grimace	42.0	Stationary and invulnerable monster that occasionally fires a blood shot at Isaac. Stops firing when room is cleared.
Vomit Grimace	42.1	Stationary and invulnerable monster that occasionally fires an Ipecac shot at Isaac. Stops firing when room is cleared.
Constant Stone Shooter	202.0	Stationary and invulnerable monster that continuously fires shots in a single direction.
Gaping Maw	235.0	Stationary and invulnerable monster that sucks Isaac towards it, along with Isaac's tears and enemy projectiles.
Broken Gaping Maw	236.0	Stationary and invulnerable monster that sucks Isaac towards it, along with Isaac's tears and enemy projectiles. Alternates between active and inactive every couple of seconds. Has a stronger attraction power than a regular Gaping Maw.
Stone Eye	201.0	Stationary and invulnerable monster that constantly rotates and fires a flickering Technology laser. Stops firing when the room is cleared.
Flesh Death's Head	286.0	Moves diagonally around the room, dealing contact damage. Releases 6 blood shots in all directions upon death. Can be killed, but also dies when the room is cleared.
Mega Clotty	282.0	Slowly moves around the room, occasionally hopping and either firing 6 blood shots in all directions, leaving a puddle of Red Creep, or spawning a Clotty or a collapsed Globin. Splits into two Clotties upon death.
Meatball	290.0	Slides around the room. If Isaac is in sight, it will stop to spew a fountain of short-range blood shots in all directions or to spit a line of damaging Red Creep towards Isaac. Spawns a Host upon death.
Mom's Dead Hand	287.0	Falls from the ceiling. Upon landing, it spawns several rock waves that travel outwards. Spawns several spiders upon death. Entering a room containing Mom's Dead Hand will warn Isaac with Mom's laugh.
Red Ghost	285.0	Disappears, then reappears near Isaac and fires a brimstone laser.
Ulcer	289.0	Pops out of the ground in random locations and spawns a Dart Fly if Isaac is in sight. Fires a blood shot after spawning 6 Dart Flies.
Suction Pitfall	291.1	Invulnerable and stationary enemy which sucks Isaac towards itself. Isaac falls into it when walked over, taking damage and popping back out after a short delay.
Blister	303.0	Slowly hops towards Isaac, occasionally spawning a Dark Ball. Spawns a Sack upon death.
Poison Mind	301.0	Slowly crawls/floats around the room diagonally, leaving a trail of damaging green creep. Explodes upon death.
Mr. Red Maw	35.2	Walks towards Isaac and attacks by launching its head towards him. Turns into a Red Maw or Gusher upon death depending on the killed body segment. Occasionally separates at will.
Nerve Ending 2	231.1	Static enemy which whips at Isaac if he gets too close.
Stoney	302.0	Chases Isaac and blocks tears, but does not deal contact damage. Temporarily pauses in exhaustion after a certain amount of time. Invulnerable; dies when the room is cleared.
Cross Stone Shooter	202.10	Stationary and invulnerable monster that continuously fires shots in four directions, alternating between cardinal and ordinal.
Portal	306.0	Spawns various enemies from the current floor until it either vanishes or is killed.
Cohort	857.0	Acts similarly to Monstro, hopping towards Isaac and can either spit a large projectile towards Isaac that bursts into 8 smaller projectiles or cough up a burst of arcing projectiles and a pile of Globin goo. Spawns 4 piles of Globin goo upon death.
Eggy	29.2	Hops aimlessly around the room, spawning slowing white creep wherever it hops. Spawns a group of Swarm Spiders upon death.
Floast	859.0	Floats diagonally around the room and is normally invulnerable. When Isaac gets close, reveals a fleshy stem that can be damaged and fires 3 blood shots in an angle at him before hiding its stem again.
Wrinkly Baby	38.3	Dashes towards Isaac at high speed and fires three blood shots in his direction once stopped.
Needle	881.0	Pops out of the ground and lunges towards Isaac, dealing contact damage.
Peeping Fatty	835.0	Has two indestructible Peeping Fatty Eyes that are out of their sockets but attached by muscles. Wanders around the room randomly, or toward Isaac if its eyes see him. Occasionally farts and fires a radial burst of 6 blood shots.
Planetoid	229.1	Moves around the room diagonally, occasionally firing blood shots that orbit itself. Fires more shots and has a chance to send its ring of shots outward upon taking damage.
Triple Grimace	42.2	Stationary and invulnerable monster that occasionally fires a triple shot at Isaac. Stops firing when room is cleared.

Degraded Bosses:

Name	ID	Notes
Blastocyst	74.0	Appears in all forms
Chub	28.0
Dingle	261.0
Envy	51.0
Fistula	71.0	Medium- and large-form only
Gemini	79.0
Gluttony	49.0
Gurdy Jr.	99.0
Gurglings	237.1
The Haunt	260.0
The Hollow	19.1
The Husk	67.1
Larry Jr.	19.0
Loki	69.0
Lokii	69.1
Lust	47.0
Mega Fatty	264.0
Mega Maw	262.0
Monstro	20.0
Pin	62.0
Polycephalus	269.0
Sloth	46.0
Teratoma	71.1
Widow	100.0
Wrath	48.0
The Wretched	100.1

Bosses


The Bloat	Daddy Long Legs	Triachnid	Lokii


Teratoma	Blastocyst	Mama Gurdy	Mr. Fred


Death	Conquest	The Fallen	Headless Horseman


Sisters Vis	The Matriarch

Double Trouble

Double Trouble Bosses


(Double Trouble) The Cage	(Double Trouble) The Fallen	(Double Trouble) The Gate	(Double Trouble) Gurdy


(Double Trouble) Loki	(Double Trouble) Little Horn	(Double Trouble) Dangle	(Double Trouble) Turdlings

Final Boss

Mom's Heart will always appear in the second floor of this chapter or in the last boss room if Curse of the Labyrinth is active. Once It Lives is unlocked, it will appear instead of Mom's Heart.


Mom's Heart	It Lives

Unlockable Achievements

Eden - Complete Chapter 4.

Pop! - Beat Chapter 4 without taking damage.

Mama's Boy - Beat Chapter 4 without taking damage.

Music

The music for the Utero is titled Viscera. The term “viscera” refers to the internal organs in the body. The Womb shares this same track.^[1]
The music for the Utero is titled Caesarian. A caesarian is a medical procedure where a baby is surgically removed from the mother due to complications during birth.^[1]
The music heard during the fight against Mom's Heart/It Lives is called Ventricide. Ventricide combines ventricle, a word that means a hollow area in an organ and is often associated with the heart, and the suffix -cide, which denotes the act of killing.

Trivia

Utero is the ablative or dative form for the Latin word and medical term "uterus", meaning "womb", and it probably stands for the expression in utero, "within the womb", which refers to certain surgical procedures or other occurrences taking place inside the womb or during the length of time that a fetus is in the uterus of the pregnant female.