Fibroids are smooth muscle tumours that arise from the muscle wall of the uterus - as such, they can generally be placed at 3 different sites: serosal (outer layer of the uterus), intramural (middle layer), or submucosal (inner layer).
Serosal fibroids can grow to a very large size without causing any symptoms. This is because the abdominal/ pelvic cavity has a lot of space for it to expand.
Submucosal ones, on the other hand, push into the uterine cavity and distort the womb lining (endometrium). The endometrium is the part that sheds at the end of every menstrual cycle, resulting in bleeding (menses). Thus, any distortion of the endometrium can result in a disturbance of the menses, either causing heavier bleeding, prolonged bleeding or irregular bleeding. Compared to serosal ones, submucosal ones can be as small as 1 cm to cause menstrual disturbances.
Intramural fibroids sit in between and if they grow, can either elongate the uterine cavity or start pushing against the endometrium. In this way, they may also cause the menses to be heavier.
If you have fibroids as large as 6cm and do not have any change in menstrual pattern, they are unlikely to be submucosal in location at the moment.
Dr Fong Yoke Fai