The uterus is a pretty special place: If you’re trying for kids, it’s where an embryo implants and where a baby eventually develops.
When something disrupts the typical development of the uterus, it’s considered an anomaly. (The same term can apply to anything that disrupts the typical development of the cervix, ovaries, or fallopian tubes.) There are also uterine anomalies that aren’t present at birth but instead happen over time.
Here, we’ll cover both congenital (before birth) and acquired (over time) uterine anomalies — as well as other uterine, ovarian, cervical, and tubal issues — and how they may play a role in fertility and pregnancy.
What are uterine anomalies and why do they occur?
“Uterine anomalies can range from congenital (occurred during development of the ‘female’ genital tract while in-utero) to acquired,” says Dr. Temeka Zore, an OB-GYN and reproductive endocrinologist (REI) at Spring Fertility.
Dr. Zore explains that uterine anomalies can be broken down into two categories:
- Congenital uterine anomalies happen when an infant assigned female at birth is developing and the two small tubes that form the fetal uterus (known as Mullerian ducts) don't fuse together seamlessly. (You might see these also referred to as Mullerian duct anomalies or uterine malformations.)
- Acquired uterine anomalies typically develop over time or as a result of uterine trauma.
“The underlying etiology of congenital uterine anomalies is not well known, but is likely polygenic (associated with multiple genes) and associated with multiple causes,” says Dr. Zore. This study supports Dr. Zore’s insight: Researchers found that uterine anomalies could be traced back through the family line based on multiple genes, and that polygenic inheritance was one of the many factors.
Overview of congenital uterine anomalies
Congenital uterine anomalies (CUAs for short) typically involve the overall structure of the uterus. Uterine anomalies that happen in the womb typically cause no symptoms, which leads to diagnosis later in life. A transvaginal 3D ultrasonography is said to be the best initial evaluation for uterine anomaly.
Even though CUAs occur in less than 5% of all people with uteruses, they may be present in up to 25% of those who have a history of miscarriage and preterm delivery. That said, research of these anomalies may be skewed given that people typically don’t experience any symptoms — and any anomaly that doesn’t get diagnosed at birth usually doesn’t present itself until someone is trying to get pregnant. Until there’s a more accurate way to diagnose anomalies before conception, that gray area of prevalence likely isn’t going anywhere.
“CUAs typically don’t directly cause infertility,” says Dr. Zore. But pregnant people with CUAs “may be at a higher risk for recurrent pregnancy loss, preterm labor/delivery, cervical insufficiency, fetal malpresentation (like breech presentation), and higher rates of needing a C-section.”
Here are the four main types of CUAs:
Septate uterus (also known as uterine septum), the most common uterine anomaly, occurs if the two Mullerian ducts don’t fuse together during fetal development, dividing an otherwise normal uterine cavity. It can be diagnosed as partial or complete. A septate uterus has been linked to a higher miscarriage rate. But treatment for a septate uterus with a hysteroscopic (done within the uterus and without external incisions) septum removal has been shown to improve pregnancy outcomes.
A bicornuate uterus, which is rare, occurs due to failure of fusion of the upper portion of the endometrial cavity. This creates two cavities that meet in the lower portion of the uterus. (While some people refer to this as a “heart-shaped uterus” that’s not a medically accurate term, according to Dr. Zore.)
One small study found that out of 56 pregnant people with bicornuate uteruses, 14 had preterm births, 14 had early miscarriages, and two had late miscarriages.
In a unicornuate uterus, only half of the uterus develops, leaving one fallopian tube. It’s smaller than a typical uterus and creates a single-horned (how it looks on an ultrasound) uterus and makes up roughly 20% of all CUAs. A unicornuate uterus has been found to be associated with preterm birth and breech presentation. It’s also been linked to other reproductive issues, such as endometriosis and renal anomalies.
Also known as double uterus and uterus didelphys, a didelphic uterus is extremely rare. This happens when the Mullerian ducts remain separate instead of fusing together, creating two uteruses and two cervices. Didelphic uterus has been linked to miscarriage, preterm birth, and fetal growth restriction.
Overview of acquired uterine anomalies
Acquired uterine anomalies happen later in life, either over time or as a result of trauma. They generally appear through heavy periods, cramps, irregular uterine bleeding, and changes in bladder function (peeing frequently or leakage).
Unlike CUAs, the prevalence for acquired uterine anomalies is a bit more clear — and aside from one (Asherman syndrome), they’re a lot more common than congenital anomalies.
These are the three main types of acquired uterine anomalies:
Fibroids are benign growths that form within the tissues of the uterus and are found in up to 70% of people with uteruses. The size and location of these growths can vary among the three types of fibroids: intramural, submucosal, and subserosal. While many people with fibroids successfully get pregnant, fibroids can change the shape of the cervix or the uterus, block the fallopian tubes, or change blood flow to the uterus — all of which impact conception. Fibroids can also cause heavy periods, pain during sex, and discomfort. They may also grow in size during pregnancy, although the majority don’t.
Polyps are another common type of growth that form within the walls of the uterus, but they’re made of endometrial tissue. They’re generally smaller in size than fibroids, can also be found in the lining of the cervix, and have the potential (rarely) to be malignant. Polyps can cause abnormal uterine bleeding. While polyps have been linked to reduced pregnancy rates, this study found that a normal pregnancy is still possible. Their exact prevalence is unclear.
Asherman syndrome (aka intrauterine adhesions) is a rare condition where the endometrium (uterine lining) gets infected or injured and scar tissue builds up. Asherman syndrome can lead to absent, light, infrequent, and sometimes painful periods, as well as difficulty getting pregnant. It can also cause recurrent miscarriages and abnormal implantation of placenta. Potential causes of scar tissue in the uterus include:
- Dilation and curettage (D&C) surgical procedure
- Uterine infection like endometritis
- Surgical removal of fibroids
- C-section delivery
- Endometrial ablation (a procedure that intentionally damages the endometrium to help with heavy periods)
Other uterine, ovarian, cervical, and tubal issues
Aside from congenital and acquired uterine anomalies, there are other (maybe more familiar) issues and conditions that affect the reproductive tracts of people with ovaries:
Cervical ectropion: A cervical ectopy is a small, raw-looking area on the cervix that occurs as a result of hormonal changes. It’s very common, affecting up to 50% of people with cervices, and often seen in people who are pregnant or taking birth control. Though benign and self-resolvable, a symptom of cervical ectopy is vaginal bleeding. And any vaginal bleeding that happens during pregnancy should be checked out by a healthcare provider.
Cysts: Cysts are fluid-filled sacs that form along the ovaries. Cysts are very common and accompany as many as 2% of all pregnancies. Most are benign and will disappear over time without the need for surgery or specific treatment. Unlike polyps and fibroids, cysts typically don’t cause vaginal bleeding and most don’t cause any noticeable symptoms. Large cysts or those that rupture may lead to pelvic irritation that ranges from a dull ache to a sharp pain.
Endometriosis: Endometriosis is when tissues similar to the tissues that make up the endometrium develop outside of the uterus. It’s found in 1 in 10 people with uteruses and of reproductive age and has been linked to people with unicornuate uteruses. Areas of this tissue mimic the uterine lining and shed during the period, which can lead to scar tissue, inflammation, and bleeding that may result in pelvic pain, painful periods, painful bowel movements, or pain with urination. Inflammation can also interfere with fertility by reducing egg quality, blocking the fallopian tubes, or distorting pelvic anatomy.
Tubal subfertility: Tubal subfertility is when the fallopian tubes are blocked as a result of fluid getting stuck in the tubes or due to obstruction (via scar tissue), making it hard for the egg and sperm to meet and fertilize. It occurs in 30% of people with fallopian tubes who have trouble conceiving. Potential causes of blocked fallopian tubes include endometriosis, ectopic pregnancy, pelvic infection, tubal ligation, and sexually transmitted infections (STIs).
The bottom line
Uterine anomalies are tricky to diagnose. But if they aren’t diagnosed at birth (which they often won’t be), there are many ways a healthcare provider can diagnose them later in life. If you think you might have a congenital or acquired uterine anomaly, or any of the other reproductive tract issues outlined above, make an appointment with your doctor to talk about your concerns. They can conduct tests to confirm the condition and discuss treatment options with you (if necessary).
This article was medically reviewed by Dr. Temeka Zore, MD, FACOG, a fellowship-trained reproductive endocrinologist and infertility specialist and board-certified OB-GYN at Spring Fertility in San Francisco.