At some point in her life, nearly one in three women develops ovarian cysts. These tiny to not-so-tiny fluid-filled sacs can grow inside the ovaries at any time from infancy through menopause. For most women, however, the only ovarian cysts that actually interfere with pregnancy are those that grow so large that they cause the ovaries to twist.

There are two kinds of ovarian cysts that can be a real problem in pregnancy. One is called a cystadenoma. This type of cyst can either be filled with watery fluid, in which case it is called serous cystadenoma, or with mucus. In the latter case, it is referred to as a mucinus cystadenoma. A cystadenoma can get as large as 12 inches (30 cm) in diameter, and it could become excruciatingly painful during pregnancy.

Another kind of ovarian cyst that can be problematic during pregnancy is a chocolate cyst, also known as an endometrioma. This kind of cyst is formed as the result of endometriosis, a condition in which the tissues that usually line the uterus appear in other parts of the reproductive organs – in this case the ovaries. Chocolate cysts are called that way because they are filled with a thick brown substance that looks similar to chocolate. When this cyst ruptures, that material can spill over into the uterus.

The lining of the uterus thickens and grows during the first 14 days of a woman’s period when estrogen levels are high. The endometrioma grows, too. During pregnancy, a woman’s body produces enormous amounts of estrogen to stimulate the growth of the blood vessels and soft connective tissues feeding the baby through the placenta. All this estrogen can also fuel growth of the chocolate cyst in the ovary. The best time for treating these kinds of ovarian cysts, of course, is before pregnancy, not during it. That is why regular exams at the OB-GYN’s office are so important.

But there is another, much more common condition involving ovarian cysts that also has an impact on a woman’s ability to get pregnant and finally feel those pregnancy signs. That condition is polycystic ovary syndrome, also known as PCOS. Polycystic ovary syndrome doesn’t always cause actual ovarian cysts. In some women it is just a hormonal imbalance that causes excesses of testosterone, leading to acne and excessive hair growth. Higher than normal levels of insulin can also cause disturbances in the hormones that allow ovulation, fertilization, and implantation of the fertilized egg into the lining of the uterus.

Treating PCOS almost never involves the surgical removal of cysts. In fact, the most common and most often effective recommendation simply involves losing weight – although for many PCOS patients, this is easier said than done. Up to 90 percent of women who have PCOS can get their symptoms under control just by diet resulting in losing 2 to 5 percent of their body weight. The slight change in body mass results in just enough change in hormonal balance that ovulation, conception, and pregnancy can occur, more often than not leading to the delivery of a healthy baby.