Volume change of uterine myomas during pregnancy: do myomas really grow?

To estimate changes in uterine myoma volume during pregnancy.

Review of departmental electronic perinatal database and medical records. Canadian Task Force Classification II-3.

Obstetrical ultrasound unit in an academic tertiary care center.

One hundred-seven patients diagnosed with uterine myomas during pregnancy and who had two or more obstetrical ultrasounds in different periods of pregnancy.

We analyzed the change in volume of uterine myomas between the first half of pregnancy (up until 19 weeks), third quarter (20-30 weeks), and last quarter (31 weeks to term). The volume of largest uterine myoma was calculated using the formula Volume (mm3)=Pi/6x(length mm)x(width mm)x(height mm).

The mean age of the population was 31+/-6 years. Between the first and the second study periods, the percentage of uterine myomas that decreased in size was 55.1% (95% CI: 43-66), with a mean decrease in volume of 35%+/-4%; while the percentage of uterine myomas that enlarged was 44.9% (95% CI: 34-56), with a mean increase in volume of 69%+/-11%. Between the second and the third study periods, 75% (95% CI: 56-87) became smaller, with a mean decrease in volume of 30%+/-3%; while 25% (95% CI: 13-43) enlarged, with a mean increase in volume of 102%+/-62%.

Contrary to common belief, we found that uterine myomas commonly decrease in volume over the course of pregnancy.