A cat’s uterus is shaped like the letter Y. Two long, slender tubes called uterine horns extend from a short central body, giving it a form that looks dramatically different from the single pear-shaped uterus found in humans. In a healthy, non-pregnant cat, the entire structure is small, pinkish, and surprisingly delicate, with each horn roughly the diameter of a pencil.
The Y-Shaped Bicornuate Structure
The technical term for this shape is “bicornuate,” meaning two-horned. The two uterine horns sit side by side in the abdomen, stretching forward toward the kidneys, while the short uterine body sits further back near the bladder. The left horn tucks beneath the colon, while the right horn runs beneath the first loop of the small intestine. They meet at a junction called the bifurcation, where they merge into the uterine body before connecting to the cervix and vagina.
This design exists because cats typically carry multiple kittens per litter. Each horn functions as an independent chamber where embryos implant and develop, distributing a litter of four to six kittens across both sides rather than crowding them into a single space.
Size and Color in a Healthy Cat
In a non-pregnant adult cat, each uterine horn measures about 8.8 centimeters long (roughly 3.5 inches) and only about 8 millimeters wide. Each horn weighs around 2 grams, about the same as two paper clips. The left and right horns are nearly identical in size. The whole organ has a pinkish color and a smooth, glistening outer surface with fine blood vessels visible along its length. It looks like a thin, soft tube, and without magnification, you might mistake it for a section of intestine at first glance.
Cats that have previously given birth tend to have a uterus that appears slightly thicker and less uniform than one from a cat that has never been pregnant. The surface may look mildly segmented rather than perfectly smooth.
How Pregnancy Transforms the Uterus
The uterus changes dramatically during pregnancy, and its appearance shifts at each stage. Around 25 to 30 days into gestation, the horns develop distinct bulges, one for each developing kitten. These rounded swellings are spaced along the horn like beads on a string, giving the uterus a clearly segmented look. At this stage, a veterinarian can often feel the individual swellings through the cat’s abdominal wall.
By about 50 days (cats carry kittens for roughly 63 to 65 days), the uterus is fully distended and the individual swellings have merged together. The horns now look like continuous, tightly filled sausages, and you can no longer distinguish where one kitten ends and the next begins from the outside. A distinct band of tissue wraps around each section where the placenta attaches to the uterine wall, visible as a darker ring on the surface.
A pregnant uterus can grow to many times its non-pregnant size, eventually filling much of the abdominal cavity. The thin pinkish walls stretch and become more vascular, taking on a deeper reddish hue as blood supply increases to nourish the kittens.
What the Uterus Looks Like During a Spay
Most people encounter a cat uterus in the context of spaying, or ovariohysterectomy. During surgery, the veterinarian lifts each horn out through a small abdominal incision. The ovaries sit at the far end of each horn, appearing as small, bumpy structures. The surgeon follows each horn down to the bifurcation where the two merge, then continues to the uterine body, which ends in a short stump just in front of the bladder.
In a young, healthy cat that has never been pregnant, the horns are thin and easy to handle. In cats that have had litters, the tissue is thicker and the blood vessels along the horns are more prominent. Sometimes the horns are difficult to pull far enough out of the body to see the bifurcation clearly, so each horn may be handled separately.
Signs of a Diseased Uterus
A uterus affected by pyometra, a serious bacterial infection, looks nothing like a healthy one. Instead of thin, delicate horns, the uterus becomes massively swollen and filled with pus. The walls stretch taut, the color shifts from pink to an angry red or grayish tone, and the organ can balloon to several centimeters in diameter. In severe cases, the infected uterus resembles a string of dark, fluid-filled sausages and can weigh significantly more than normal.
Pyometra typically develops after a heat cycle, when hormonal changes cause the uterine lining to thicken and produce excess fluid. This creates an ideal environment for bacteria. A condition called cystic endometrial hyperplasia often precedes pyometra, where the inner lining develops small fluid-filled cysts that make the uterine wall appear bumpy and thickened even before infection sets in. Unspayed middle-aged and older cats are most at risk.