Ovarian cysts are fluid-filled sacs on or within an ovary, often discovered incidentally during routine prenatal ultrasound examinations. While many women are concerned, the vast majority of these masses are benign and resolve spontaneously as pregnancy advances. The presence of a cyst does not automatically threaten the health of the mother or the developing fetus. However, a small percentage may persist, grow, or lead to complications requiring careful monitoring and intervention. Understanding the types of cysts encountered during gestation and how they are managed is important for ensuring a healthy pregnancy outcome.
Identifying Ovarian Cysts During Pregnancy
Ovarian cysts are typically discovered during first-trimester dating or anomaly scans, as these procedures offer a clear view of the pelvic structures before the enlarging uterus obscures them. Cysts found in pregnancy generally fall into two main categories: functional and pathological. Functional cysts are the most frequent type and are directly related to the hormones of the menstrual cycle and pregnancy.
The most common functional cyst is the corpus luteum cyst, which forms from the follicle that released the egg. This structure produces progesterone, a hormone necessary to sustain the pregnancy until the placenta is established. These cysts are usually small, simple, and tend to disappear on their own by the early second trimester, typically around 16 to 20 weeks of gestation.
Pathological cysts are not related to the normal reproductive cycle and include types such as dermoid cysts, endometriomas, and cystadenomas. These types are less likely to resolve and may grow larger, sometimes containing complex elements. Size is a primary indicator for risk assessment. Simple cysts measuring less than 5 centimeters are generally considered low risk, while those with complex features or exceeding 5 to 6 centimeters warrant closer observation.
How Cysts Influence Maternal and Fetal Health
While most ovarian cysts are asymptomatic, larger or complex cysts can present maternal risks, with ovarian torsion being the most urgent complication. Torsion occurs when the ovary twists around the ligaments that hold it in place, cutting off its blood supply. Pregnancy increases the risk of torsion due to the rapid growth of the corpus luteum cyst in the first trimester and the displacement of the ovaries by the growing uterus, which provides more rotational freedom.
Symptoms of ovarian torsion include the sudden onset of severe, unilateral pelvic pain, often accompanied by nausea and vomiting. This condition is a surgical emergency because prolonged lack of blood flow can lead to tissue death, potentially requiring the removal of the ovary. Rupture is another potential complication, causing sudden, sharp pelvic pain that may lead to internal bleeding or localized inflammation depending on the cyst’s contents.
In later pregnancy stages, a large, persistent cyst (10 centimeters or more) can potentially cause an obstruction. If the mass is positioned low in the pelvis, it may block the birth canal, a rare condition called dystocia, making vaginal delivery difficult or impossible. Direct risks to the fetus from the cyst itself are minimal. The risk to the baby primarily arises indirectly from severe maternal complications, such as infection following rupture or the need for emergency surgery.
Medical Approaches to Monitoring and Treatment
The standard approach for a small, simple, and asymptomatic ovarian cyst discovered during pregnancy is expectant management, often called “watch and wait.” This protocol involves monitoring the cyst with repeat ultrasound examinations, typically around 16 weeks of gestation, to confirm resolution or size decrease. This conservative approach is preferred because the vast majority of functional cysts disappear on their own, and intervention carries inherent risk to the pregnancy.
Intervention is reserved for specific circumstances, such as when a cyst causes persistent, severe pain, shows signs of acute complications like torsion or rupture, or has complex features suggesting potential malignancy. The size of the cyst is a major factor; masses larger than 10 centimeters often warrant removal due to the elevated risk of complications.
If surgical removal is necessary, the safest time to perform the procedure is generally during the second trimester, between 14 and 23 weeks of gestation. Operating during this window avoids the high miscarriage risk associated with the first trimester and the difficulty of accessing the pelvis due to the large uterus in the third trimester. Surgeons typically favor a minimally invasive laparoscopic approach. However, a traditional open surgery (laparotomy) may be necessary for very large or highly complex masses.