Uterine myomas don't grow during pregnancy

In fact, they commonly decrease in volume, according to observations made on 107 pregnant women with myomas visiting an obstetrical ultrasound unit in an academic tertiary care center.

Ahmad Hammoud, MD, and colleagues found that a little more than half the myomas studied (55.1%; 95% CI; 43–66) decreased in size by about one third (35% ± 4%) between the first half of pregnancy (up to 19 weeks) and the third quarter (weeks 20–30), while 44.9% (95% CI; 34–56) enlarged by a mean of 69% ± 11%.

Between the third and fourth quarters of pregnancy, 75% of the myomas shrunk (95% CI; 56–87) with a mean decrease in volume of 30% ± 3%, while one quarter (25%; 95% CI; 13–43) enlarged by a mean of 102% ± 62%.