A woman has one uterus. It’s a single, hollow, pear-shaped organ that sits in the pelvis between the bladder and the rectum. The uterus is where a fertilized egg implants and grows into a fetus, and its lining sheds each month during a menstrual period. While one uterus is the standard, a small number of women are born with two, and others have had theirs surgically removed.
What the Uterus Does
The uterus has two primary jobs: managing your menstrual cycle and supporting pregnancy. Each month, the inner lining (called the endometrium) thickens to prepare for a potential pregnancy. If no fertilized egg implants, the uterus sheds that lining, which is your period. The cramping you feel during menstruation is the uterus contracting to push out the tissue.
When conception does happen, the fertilized egg travels down a fallopian tube and embeds itself in that thickened lining. The uterus then stretches dramatically over nine months to accommodate the growing fetus, expanding from roughly the size of a fist to the size of a watermelon.
Can a Woman Have Two Uteri?
Yes, though it’s uncommon. A condition called uterus didelphys means a woman is born with two separate uteri, each with its own cavity. This happens during fetal development when two tubes that normally fuse into a single uterus instead remain separate. Some women with the condition also have two cervixes or two vaginal canals.
Most women with a double uterus never know they have one. The condition often causes no symptoms at all and is discovered incidentally during a routine pelvic exam or imaging for another issue. One telltale sign, though, is menstrual bleeding that continues even with a tampon in place. This happens because the tampon sits in one vaginal canal while blood flows from the second uterus through the other canal.
Repeated miscarriages can also prompt the discovery. Imaging to investigate pregnancy loss sometimes reveals the two separate uterine cavities for the first time.
Other Uterine Variations
Uterus didelphys is just one type of congenital uterine difference. Others include a bicornuate uterus (heart-shaped, with a deep indentation at the top), a septate uterus (a single uterus divided by a wall of tissue), and a unicornuate uterus (only one half developed). Together, septate and bicornuate uteri account for nearly two-thirds of all congenital uterine differences.
These variations are typically identified through imaging. MRI is considered the gold standard, with reported accuracy up to 100% for classifying the type of anomaly. Ultrasound can also detect many of these differences. An older method called hysterosalpingography, which uses dye and X-rays to outline the uterine cavity, can spot that something is unusual but struggles to distinguish between specific types. Its accuracy for telling a septate uterus from a bicornuate one is only about 55%.
Pregnancy With a Double Uterus
Women with two uteri can and do have healthy pregnancies, but the risks are higher than average. Each individual uterine cavity is smaller than a typical single uterus, which limits the space a baby has to grow. The specific complications linked to a double uterus include miscarriage, preterm labor, low birth weight, growth restriction, breech positioning, and a higher likelihood of needing a cesarean delivery.
In rare documented cases, a woman with uterus didelphys has carried a separate pregnancy in each uterus at the same time. Each uterus can contract independently, which has occasionally led to deliveries days or even weeks apart. One reported case involved a 66-day gap between the birth of each twin.
Women With No Uterus
On the other end of the spectrum, millions of women have zero uteri following a hysterectomy. CDC data from 2021 shows that 14.6% of women aged 18 and older in the United States have had their uterus surgically removed. That percentage climbs sharply with age: about 2.8% of women between 18 and 44, 22.1% of those 45 to 64, and 41.8% of women 75 and older. A hysterectomy is performed for a range of reasons, including fibroids, endometriosis, chronic pain, and cancer. After the procedure, menstruation stops permanently and pregnancy is no longer possible.
A much smaller number of women are born without a uterus entirely, a condition known as Mayer-Rokitansky-Küster-Hauser syndrome. These women have functioning ovaries and typical external development but no uterine cavity.