Ovarian cysts may occasionally be present during pregnancy. One of the main reasons for performing an internal examination at the beginning of a pregnancy is to ensure that the ovaries are normal as well as the uterus, vagina and the structure of the bony pelvis.
The ovaries always develop small cysts (up to 2 cm. in diameter) during pregnancy and these are of no consequence. The corpus luteum also enlarges the ovary and may sometimes become cystic. Occasionally, however, a large ovarian cyst measuring several centimetres in diameter is found in early pregnancy. When a cyst of this size is discovered it is generally removed at the first reasonable opportunity. Because the cyst may be situated in the same ovary as the corpus luteum, and damage to the corpus luteum may cause miscarriage, the removal of the cyst by operation is usually deferred until after the end of the 14th week of pregnancy. By this time the placenta has taken over the hormone-producing functions of the corpus luteum. After the ovarian cysts are surgically removed the ovary is reconstructed so that it will again function normally.
Operation is advisable because ovarian cysts may undergo twisting or torsion, and if this happens later in pregnancy not only is the operation extremely difficult, but the woman might rapidly become very seriously ill before it could be performed.
There is always a possibility that an operation for the removal of an ovarian cyst during pregnancy will precipitate a miscarriage. This does not often happen but it is a chance that has to be taken and is a much smaller risk to the woman and her baby than the danger of the cyst twisting at a later stage of the pregnancy.