Pregnancy has a definite effect on fibroids, though there's no way to predict how things will play out. It does appear that most fibroids don't become larger during pregnancy. The link between pregnancy and fibroid growth may have something to do with the genetic makeup of individual fibroids along with the kind and amount of growth factors that are present in the mother's blood.
One ultrasound study performed on pregnant women with sizeable fibroids found that 69% of them experienced no increase in fibroid growth during the course of their pregnancies. In the women who did experience an increase in the size of their fibroids (31%) the growth occurred as a spurt that was limited to the first trimester. Furthermore, the fibroids almost always shrank after delivery.
Fibroids are a very common occurrence in women who are in their late thirties and forties. Because women are having babies at a later age, fibroids have been causing more difficulties than were seen in the past. They are a common cause of infertility and if a woman does become pregnant, can cause problems with the pregnancy, too.
Most women who find they are pregnant and have fibroids experience no difficulties. Studies have not found absolute proof that fibroids cause early labor or delivery or fetal abnormalities. On the other hand, the risk for cesarean section is much higher in women with fibroids.
While a woman is pregnant, the placenta produces a lot of the female hormones that can cause preexisting fibroids to grow. In rare cases, the fibroids grow very fast so that the blood vessels are unable to deliver enough oxygen to the fibroid tissues, causing the fibroid cells to degenerate. The degeneration of fibroids can be painful but doesn't often take long to resolve. No treatment is necessary in such a case and no harm is caused to the developing infant.
During this time, a woman may experience some mild contractions, though it is quite rare for actual labor to begin. Despite the tendency for a good outcome in such a case, it's important that a pregnant woman who has fibroids contacts her physician if she has any pain or possible contractions. Most of the time, bed rest, a hot water bottle, and pain killers will be all that is necessary for treatment, but sometimes, the doctor will decide to give medication to stop the contractions.
Sometimes, not too often, a fibroid will grow quite close to the cervix during a woman's pregnancy. If the fibroid is large, it may pose an obstacle to the baby as it tries to journey through the birth canal. If the baby seems to find it difficult to get through the birth canal, an ultrasound may be performed and health care providers will discover the fibroid that is blocking the baby's exit. In this case, a c-section must be performed.