An ovarian cyst is a fluid-filled sac that develops on or within an ovary. When discovered during pregnancy, these masses are a common finding, often detected incidentally during a routine early ultrasound. The vast majority are benign and pose no threat to the mother or the developing fetus. Most cysts resolve on their own without the need for intervention over the course of the pregnancy.
Types of Ovarian Cysts Common During Pregnancy
The most frequently encountered ovarian cyst in early pregnancy is a functional cyst, known as the corpus luteum cyst. This structure is a normal, temporary gland that forms from the follicle that released the egg during ovulation. It produces the hormone progesterone, which supports the uterine lining until the placenta is fully developed to take over the function, typically around 10 to 12 weeks of gestation. This hormone production is necessary for maintaining the pregnancy during the first trimester.
A corpus luteum cyst develops if this temporary gland fills with fluid or blood instead of shrinking after conception, sometimes growing between 2 to 10 centimeters. It remains a physiological structure necessary for the early stages of fetal development. These cysts are benign and are expected to spontaneously regress by the second trimester, often around 16 to 20 weeks.
Other cysts found during pregnancy are categorized as pathological or non-functional. These include dermoid cysts (mature cystic teratomas), which are growths containing various tissues like hair, fat, or bone. Endometriomas, or “chocolate cysts,” result from endometriosis tissue growing on the ovary. While these non-functional cysts are less likely to resolve spontaneously, they are benign and are monitored closely throughout the pregnancy.
How Ovarian Cysts are Monitored
The primary approach to managing an ovarian cyst found during pregnancy is expectant management. This conservative strategy is employed because most cysts are functional and resolve naturally, avoiding unnecessary intervention during gestation. The decision to monitor is based on specific criteria determined by imaging and the absence of symptoms.
For a cyst to be managed conservatively, it should typically be asymptomatic and appear “simple” on ultrasound, meaning it is purely fluid-filled without solid components. Cysts smaller than 5 to 6 centimeters in diameter are usually benign functional cysts that will disappear spontaneously. These smaller, simple cysts often require no further follow-up outside of routine prenatal care.
If a cyst is larger than 5 to 6 centimeters, or if it presents with complex features like septations or solid areas, monitoring becomes more rigorous. Serial ultrasounds are used to track the cyst’s size and internal appearance over time. This assessment is often timed for the early second trimester to allow for the natural resolution of any corpus luteum cysts before the enlarging uterus makes imaging more difficult. The goal of this surveillance is to confirm the cyst’s benign nature and stability, prioritizing the safety of the mother and fetus.
Recognizing and Managing Complications
While most ovarian cysts are harmless, they can occasionally lead to acute complications requiring immediate medical attention. The two main acute events are ovarian torsion and cyst rupture, both presenting with severe symptoms. Ovarian torsion occurs when the ovary twists around its supporting ligaments, cutting off its blood supply. This is most likely to happen between 10 and 17 weeks of gestation.
Ovarian torsion symptoms include the sudden onset of severe, sharp, unilateral lower abdominal pain, often accompanied by nausea and vomiting more intense than typical morning sickness. Cyst rupture typically causes sudden, moderate-to-severe pain, which may subside as the internal fluid is absorbed. If the rupture involves significant internal bleeding, symptoms such as dizziness, weakness, or signs of shock may occur, necessitating emergency care.
If confirmed ovarian torsion occurs, emergency surgery is necessary to untwist the ovary and restore blood flow. The procedure is aimed at preserving the ovary through detorsion, and if the cyst is the cause, removing only the cyst (cystectomy) is preferred over removing the entire ovary. If a cyst is large, complex, or highly suspicious for malignancy based on imaging, elective surgical removal is often planned for the second trimester (14 to 20 weeks). This window is considered the safest time for surgery, as the risk of miscarriage is lower than in the first trimester, and the procedure is less complicated than in the late third trimester.