Ovarian cysts are relatively common during pregnancy, with adnexal masses reported in up to 4% of pregnant women. An ovarian cyst is a fluid-filled sac that forms inside or on the surface of an ovary. Most cysts found during pregnancy are benign, resolve on their own, and do not cause complications. Cysts are typically classified into two main categories: functional, which are related to the normal menstrual cycle and hormonal changes, and pathological, which are not.
The most frequently encountered type is the corpus luteum cyst, which is formed from the follicle that released the egg during ovulation. This structure, the corpus luteum, is necessary in early pregnancy because it produces the hormones progesterone and estrogen to sustain the pregnancy. The placenta usually takes over hormone production around 10 to 12 weeks of gestation. If the corpus luteum fills with fluid instead of breaking down, it forms a cyst that can persist into the second trimester. These functional cysts are usually small, less than 5 cm in diameter, and often spontaneously disappear by 16 to 20 weeks of gestation.
Follicular cysts are another type of functional cyst that can occur when a follicle fails to rupture and release an egg, instead filling with fluid. Pathological cysts, however, are not related to the menstrual cycle and were often present before the pregnancy but are only detected now. Examples include dermoid cysts, which are growths containing various tissues like hair or fat, and endometriomas, often called “chocolate cysts,” which are caused by endometriosis. While functional cysts are expected to shrink, pathological cysts may persist or continue to grow during the pregnancy.
How Ovarian Cysts Are Detected
The detection of an ovarian cyst in pregnancy is most often an incidental finding during routine prenatal care. With the widespread use of ultrasound for dating and viability assessments, many cysts are discovered early in the first trimester. The ultrasound provides a clear image, allowing healthcare providers to determine the cyst’s size, location, and whether it is simple (filled with fluid) or complex (containing solid components or septations). Simple cysts that are smaller than 5 cm are generally considered low-risk and often require no further immediate evaluation.
A cyst may also be discovered when a pregnant woman experiences symptoms that prompt further investigation. Although many cysts are asymptomatic, a growing or complicated cyst can cause non-specific symptoms like mild pelvic pain, discomfort, or a feeling of abdominal fullness. These symptoms can sometimes be mistaken for common pregnancy discomforts, which may delay a specific diagnosis. If the initial ultrasound findings are unclear or if the cyst is large and complex, a Magnetic Resonance Imaging (MRI) scan may be used to gain a more detailed view, as it is considered safe after the first trimester.
Potential Risks and Complications
While most ovarian cysts are benign, a small percentage can lead to acute complications requiring immediate medical attention. Ovarian torsion is a primary risk, occurring when the ovary twists around its supporting ligaments and cuts off its blood supply. This condition is more likely with larger cysts, especially those with solid components like dermoid cysts. Torsion typically presents as sudden, severe abdominal or pelvic pain, often accompanied by nausea and vomiting, and the risk is highest during the first trimester and immediately after delivery.
Another complication is cyst rupture, which occurs when the fluid-filled sac bursts, releasing its contents into the abdominal cavity. Rupture of a simple functional cyst is common and usually causes temporary, sudden pain managed with medication. However, the rupture of a pathological or hemorrhagic cyst can lead to more significant internal bleeding and severe, persistent pain. In rare cases, a very large ovarian cyst detected late in pregnancy can interfere with the baby’s descent into the pelvis. If the mass physically obstructs the birth canal, a Cesarean section may be necessary.
Monitoring and Treatment Approaches
The standard approach for managing an ovarian cyst identified during pregnancy is “watchful waiting,” particularly for cysts that appear simple and are small in size. For asymptomatic cysts under 5 to 6 cm in diameter, the patient is monitored with serial ultrasounds to track the cyst’s size and appearance. This conservative management is preferred because the majority of functional cysts will spontaneously regress by the second trimester, and intervention carries a small risk to the pregnancy.
If a patient experiences discomfort or mild pain from the cyst, conservative measures such as rest and pain relief, often with acetaminophen, are typically recommended. Surgical intervention is generally reserved for specific, high-risk scenarios, such as suspected ovarian torsion, cyst rupture with significant bleeding, or a cyst that shows features suggestive of potential malignancy. Non-emergency surgery to remove a persistent or growing pathological cyst is ideally scheduled during the second trimester, specifically between 16 and 23 weeks of gestation.
The second trimester is considered the safest window for surgery because the risk of miscarriage is lower than in the first trimester. Additionally, the uterus is not yet large enough to significantly complicate the surgical approach. Surgeons often use minimally invasive laparoscopy for cyst removal, when appropriate, which helps to reduce recovery time and minimize uterine manipulation. The goal of any intervention is to protect the health of the mother and the fetus while removing the complication-prone or suspicious mass.