Blood clots in the ovaries, known medically as ovarian vein thrombosis (OVT), most commonly occur after childbirth. They can also develop from pelvic infections, gynecological cancers, fertility treatments, and recent abdominal surgery. The condition is rare, affecting roughly 1 in 600 to 1 in 2,000 pregnancies, but it can become serious if the clot travels to the lungs or grows into surrounding veins.
Postpartum Recovery Is the Leading Cause
The most common trigger for ovarian blood clots is the postpartum period, particularly the days and weeks following delivery. During pregnancy, the body naturally shifts toward a more clot-prone state to prevent dangerous bleeding during birth. Blood volume increases, hormonal changes make blood thicker, and the enlarged uterus compresses pelvic veins, slowing blood flow. After delivery, these factors don’t immediately reverse, leaving a window where clots can form in the ovarian veins.
Cesarean sections carry a notably higher risk. OVT has been reported in about 2% of C-section deliveries, compared with 0.05 to 0.18% of vaginal births. The surgical trauma, longer recovery with reduced mobility, and additional tissue inflammation all contribute to that gap. Most postpartum cases develop on the right side, likely because the right ovarian vein is longer and blood flow patterns make it more susceptible to stagnation.
Pelvic Infections and Inflammation
Infections in the pelvic region can damage the walls of nearby veins, triggering the clotting process. Pelvic inflammatory disease, which typically results from sexually transmitted bacteria spreading to the uterus and fallopian tubes, is one established risk factor. Endometritis (infection of the uterine lining), intra-abdominal infections, and sepsis can all set off a similar chain of events. When infection and inflammation occur near the ovarian veins, the immune response activates clotting proteins locally, and the combination of vein wall injury and sluggish blood flow creates the conditions for a clot to form.
Inflammatory bowel disease, particularly during active flare-ups, has also been linked to ovarian vein thrombosis. Chronic inflammation anywhere in the abdomen can shift the body’s clotting balance, making pelvic veins vulnerable.
Ovarian Cancer and Gynecological Tumors
Ovarian cancer carries one of the highest rates of blood clot complications among all gynecological cancers. Between 10 and 30% of ovarian cancer patients experience some form of venous blood clot, and having one is associated with a two- to three-fold higher risk of death.
Tumors promote clotting through several pathways at once. Cancer cells release substances that directly activate the clotting cascade, causing blood to thicken and platelets to clump. Inflammatory molecules produced by the tumor damage the inner lining of blood vessels. Large pelvic masses and fluid buildup in the abdomen physically compress the iliac and femoral veins, slowing blood flow to a crawl. On top of all that, the surgeries and chemotherapy used to treat the cancer further weaken blood vessels and increase clot risk.
Advanced-stage ovarian cancer (stages III and IV) poses the greatest danger, largely because of the higher tumor burden and widespread inflammation. Certain subtypes, particularly clear cell and mucinous carcinomas, are especially prone to triggering clots because they produce higher levels of clot-promoting proteins.
Fertility Treatments and Hormonal Stimulation
Women undergoing IVF face an elevated risk of blood clots when ovarian hyperstimulation syndrome (OHSS) develops. This condition occurs when fertility medications cause the ovaries to swell dramatically and leak fluid into the abdomen. The incidence of clotting complications runs at about 0.2% across all IVF cycles but jumps to as high as 10% in severe OHSS cases, making it the most dangerous complication of the syndrome.
OHSS shifts the blood into a hypercoagulable state through multiple changes in clotting factors. Interestingly, the clots that form during OHSS don’t always appear in the pelvis. Venous clots account for 67 to 75% of cases, and they disproportionately affect the upper body, including the arms and neck. This unusual pattern may be explained by high concentrations of estrogen draining upward through lymphatic channels from fluid trapped in the abdomen. The remaining 25 to 33% of clots are arterial, often occurring in the brain.
Pelvic and Abdominal Surgery
Any surgery in the pelvic or abdominal area can increase the risk of ovarian vein clots. The combination of tissue damage, post-surgical inflammation, and reduced movement during recovery creates a fertile environment for clotting. Gynecological procedures like hysterectomy and tumor removal carry particular risk because they involve the veins closest to the ovaries. The longer and more complex the surgery, the greater the exposure.
Symptoms and How It’s Found
Ovarian vein thrombosis can be tricky to identify because its symptoms overlap with many other abdominal conditions. The most common presentation is lower abdominal or pelvic pain, often on the right side, sometimes accompanied by fever. In postpartum cases, a tender mass may be felt in the lower right abdomen. Because these symptoms can mimic appendicitis, kidney stones, or ovarian torsion, the condition is frequently discovered only after imaging for another suspected diagnosis.
CT scans are the primary tool for diagnosis. In many reported cases, the clot is found incidentally when a scan performed for abdominal pain reveals an unexpected blockage in the ovarian vein. MRI can also visualize the clot, but CT is more commonly used as the first-line imaging study because of its speed and availability.
How Ovarian Blood Clots Are Treated
Treatment centers on blood thinners, typically a type of injectable anticoagulant given for one to three months. In one case series of 18 patients, 72% received this duration of treatment and only one experienced a recurrence, suggesting it’s an effective approach for most people. No firm international guidelines exist for managing ovarian vein thrombosis specifically, so treatment decisions are often adapted from protocols for blood clots in other veins.
The main concern during treatment is preventing the clot from extending into larger veins or breaking loose and traveling to the lungs, which would cause a pulmonary embolism. Most patients recover fully with anticoagulation alone. The condition rarely requires surgical intervention, though ongoing monitoring with imaging helps confirm the clot is shrinking as expected.