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

Study objective: To estimate changes in uterine myoma volume during pregnancy. Design: Review of departmental electronic perinatal database and medical records. Canadian Task Force Classification II-3. Setting: Obstetrical ultrasound unit in an academic tertiary care center. Patients: One hundred-seven patients diagnosed with uterine myomas during pregnancy and who had two or more obstetrical ultrasounds in different periods of pregnancy. Interventions: 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) = Π/6 × (length mm) × (width mm) × (height mm). Measurements and main results: 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%. Conclusion: Contrary to common belief, we found that uterine myomas commonly decrease in volume over the course of pregnancy.