A fibroid is an abnormal growth in the uterus. We also call them myomas. I say abnormal because a fibroid shouldn't be there, however so many women have fibroids we consider them common. How common are they? At least 30% of women have fibroids. I have recently heard that some say that up to 60-70% of women have fibroids, although that sounds a little high to me.

How do they get there? We don’t know how they start. We do know that they grow in response to estrogen. They are not seen prior to puberty and get smaller after menopause. It seems that each fibroid starts as one fibroid cell, and this cell keeps dividing resulting in a large fibroid. Even though they come from the cells of the uterus, they do look different than the normal uterine muscle. They are whitter because they have few blood vessels, and they are firmer, about the consistency of a potato. We don’t know why some women have only one; some have 40.

Fibroid size and a word about centimeters. Most medical things are measured in centimeters (cms). One cm equals 2.54 cms. So a 5 cm fibroid is about 2 inches. A tennis ball is about 6.5 cms. How does this compare to the size of the uterus? The uterus, not including the cervix, is about 5 cms tall, 2.5 cms thick and about 5 cms wide. So a 5-6 cm fibroid is about the size of the uterus. A bigger fibroid would be bigger than the uterus. A 10 cm fibroid is a lot bigger. I commonly find fibroids on ultrasound and as I point them out to my patients they say ”wow, that’s big”. But something that looks big on ultrasound may be really a more medium sized and not a problem. Every doctor has a different view on the minimum fibroid size they consider tolerable. It’s usually around 5-6 cms, but it also depends greatly on the location.

Location. It’s either subserosal, intramural or submucus. Patients ask all the time, “is it growing in the wall?” They all are growing in the wall to some degree. The wall means the muscle of the uterus and that’s where fibroids mostly come from. It’s just a matter of how they grow after they start in the wall.

Some are loosely anchored in wall, more towards the outside, but have most of their growth on the outside of the uterus. These are called subserosal (the subserosa is the thin outside layer of the uterus). Some of these become pedunculated, which means they hang like a ball on a short thick string.

Some are mostly intramural, but the wall of the uterus is only about 1 cm thick. So as the fibroid grows bigger than 1 cm, it will bulge either inward or outward (becoming more submucusal or subserosal)

Some grow from the uterine wall but mostly bulge into the inside of the uterine cavity. Now the inside of the uterus is lined with the glandular cells called the endometrium. These are the cells that shed with menstruation. These are the cells that provide a nice place for an embryo to get started. This is the same endometrium that is measured during induction of ovulation and IVF. A fibroid will disrupt the endometrium. It will stretch the lining and cause gaps in the lining, and this leads to abnormal bleeding. More on fibroids to come,

Dr. Licciardi