When a female fetus develops fluid-filled sacs on their ovaries that are more than 2cm in size, this is called a fetal ovarian cyst.
Fetal ovarian cysts happen because the fetus in the womb is exposed to pregnancy-related hormones from the mother and the placenta. The ovary reacts to these hormones by making cysts. This happens in one of about every 2,500 live births.
Fetal ovarian cysts are diagnosed by ultrasound. They should also be followed with ultrasounds throughout the pregnancy to see if they change. Occasionally, MRI may be done to look at the cysts as well. Fetal ovarian cysts are not genetic, therefore genetic testing does not need to be done for this reason alone.
Fetal ovarian cysts can have complications such as bleeding into the cyst or twisting of the cyst (called torsion). Babies with ovarian cysts can sometimes develop problems with a blockage of other organs from the cyst. If there is a blockage of the bowels, this may affect the baby’s ability to swallow before birth and cause extra amniotic fluid around the baby, this is called polyhydramnios.
After the baby is born she will need to have the cyst monitored, usually by ultrasound. Most cysts go away on their own in the months after birth. Sometimes the baby will need surgery for the cyst. Surgery may be recommended if the cyst is causing the baby symptoms (such as pain), if the cyst is very large, or if the cyst does not go away over time.
In some babies, the cyst will lead to damage to the ovary and it will not function normally. This often means that the baby will have only one normal ovary. Women with one ovary still go through puberty and are able to have children.
Having one baby with fetal ovarian cysts does not put you at increased risk for this to happen in another pregnancy.
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Last updated September 2019
