We enrolled 4,582 women of whom 4,271 had ultrasounds and were enrolled for the first time (). Women who did not complete an ultrasound (n=311) were similar to those who did in terms of maternal age, race/ethnicity, parity, marital status and education level. Ultrasounds were completed an average of 61 days ±13 days from self-reported LMP. Leiomyoma prevalence did not differ by gestational age at ultrasound (p=0.3).
Characteristics of First Trimester Cohort Screened by Ultrasound for Uterine Leiomyomas
The prevalence of one or more leiomyomata was 10.7% (95% confidence interval (CI): 8.5, 13.6). Among 458 women with one or more leiomyomata, we identified a total of 687 leiomyomata. Maximum leiomyoma diameter ranged from 0.5cm to 12.9cm. The mean size of the women’s largest leiomyoma was 2.3cm (95% CI 1.8 to 2.8cm). Subserosal (42%) and intramural (35%) leiomyomata were most common; 17% were submucous, and 5% were pedunculated. Nearly half of all leiomyomata occurred in the uterine corpus and 35% were in the fundus. Leiomyomata were evenly distributed in anterior and posterior as well as on the right and left sides of the uterus (p=0.2). Leiomyoma type and location did not differ between blacks and whites (p≥0.1 for each comparison) except that black women had slightly more leiomyomata in the posterior wall of the uterus than white women (p=0.03). Seventy-two percent of women with a leiomyoma did not report a diagnosis of leiomyomata prior to this pregnancy.
Although overall leiomyoma prevalence was 10.7%, prevalence differed by race/ethnicity. Black women (n=915) had a prevalence of 18% (95% CI: 13, 25); white women (n= 2,826), 8% (95% CI: 7, 11); Hispanic women (n=335), 10% (95% CI: 5, 19); and the “other” group, predominantly Asian (n=186), 13% (95% CI: 10, 16). Leiomyomata were present in women as young as 19 years old. For black and white women we had sufficient numbers of participants to examine differences with age. Prevalence among those under 25 years old was 6% (95% CI: 3, 10) in black women and 4% (95%CI: 3, 7) in whites. Prevalence increased with age for both blacks and whites (). The rise in prevalence by age was steeper among black women (p=0.02).
Prevalence of Uterine Leiomyomas among Black (n=915) and White Women (n=2826)*†
Among those with leiomyomata, having two or more leiomyomata also differed by race/ethnicity: 39% of black women with leiomyomata had multiple tumors (95% CI: 37, 42), 20% of white women (95% CI: 20, 21), and 22% of Hispanic women (95% CI: 11, 42). The presence of multiple tumors increased with age for black women from 22% (95% CI: 14, 35) for women younger than 30, to 58% (CI 52, 65) for women 35 years and older. For white women, the proportion with multiple tumors increased slightly across age from 19% (95% CI: 16, 22) in women younger than 30 to 25% (95% CI: 22, 29) for women 35 years and older (). This difference in the proportion of women with multiple tumors as age advances was significantly different between blacks and whites (p=0.005).
Percentage of Women with More Than One Leiomyoma among Those with Leiomyomas
Average size of the women’s largest leiomyoma differed by race/ethnicity as well. Average size was 2.5cm (95% CI: 2.1, 3.1) for black women. This was not different from the average leiomyoma size for Hispanics, 2.4cm, (95% CI: 1.8, 3.1), but significantly larger than average leiomyoma size for white women, 2.0cm, (95% CI: 1.6, 2.4, p=0.0002). Leiomyoma size tended to be larger in older compared with younger black women, but there was little variation in size with age for whites. However, the difference between blacks and whites was not statistically significant (p=0.08).
Prevalence estimates are intrinsically determined by the operational definition of the size of a leiomyoma required to classify a mass as a leiomyoma. If we were to define prevalence based on the original Muram criteria restricting leiomyoma diameter to ≥3.0cm, prevalence is 7% in black (95% CI: 5, 10) and 3% in white women (95% CI: 2, 3), p<0.001. Another common cut-point, requiring a diameter of ≥1.0cm, results in prevalence of 16% in black (95% CI: 12, 22) and 7% in white women (95%CI: 6, 9), p<0.001.