Self-report versus ultrasound measurement of uterine fibroid status

Abstract

Background: Much of the epidemiologic research on risk factors for fibroids, the leading indication for hysterectomy, relies on self-reported outcome. Self-report is subject to misclassification because many women with fibroids are undiagnosed. The purpose of this analysis was to quantify the extent of misclassification and identify associated factors.

Methods: Self-reported fibroid status was compared to ultrasound screening from 2046 women in Right From The Start (RFTS) and 869 women in the Uterine Fibroid Study (UFS). Log-binomial regression was used to estimate sensitivity (Se) and specificity (Sp) and examine differences by ethnicity, age, education, body mass index, parity, and miscarriage history.

Results: Overall sensitivity was ≤0.50. Sensitivity was higher in blacks than whites (RFTS: 0.34 vs. 0.23; UFS: 0.58 vs. 0.32) and increased with age. Parous women had higher sensitivity than nulliparae, especially in RFTS whites (Se ratio=2.90; 95% confidence interval [CI]: 1.51, 5.60). Specificity was 0.98 in RFTS and 0.86 in UFS. Modest ethnic differences were seen in UFS (Sp ratio, black vs. white=0.90; 95% CI: 0.81, 0.99). Parity was inversely associated with specificity, especially among UFS black women (Sp ratio=0.84; 95% CI: 0.73, 0.97). Among women who reported a previous diagnosis, a shorter time interval between diagnosis and ultrasound was associated with increased agreement between the two measures.

Conclusions: Misclassification of fibroid status can differ by factors of etiologic interest. These findings are useful for assessing (and correcting) bias in studies using self-reported clinical diagnosis as the outcome measure.

FIG. 1.

Self-report sensitivity (upper panel) and specificity (lower panel) by race/ethnicity and age at interview for Right From The Start (RFTS, n=2046) and Uterine Fibroid Study (UFS, n=869) participants. Error bars indicate 95% confidence intervals (CI). Estimates for the following RFTS age groups are excluded because there were fewer than 10 women in each race/age category: sensitivity for women aged 18–24 years and black women over 40 years; specificity for black women aged 40–44 years.

FIG. 2.

Association of demographic and reproductive factors with sensitivity of self-reported uterine fibroid status among 279 RFTS and 507 UFS participants with fibroids detected at study ultrasound. Sensitivity ratios (sensitivity in a subgroup of interest compared to sensitivity in the reference group) are adjusted for age (continuous), parity, and (for unstratified estimates) race/ethnicity. A quadratic term was entered for age in the UFS multivariate analysis due to nonlinearity. ^aAmong women with a previous pregnancy. ^bEstimates obtained using Poisson regression.

FIG. 3.

Association of demographic and reproductive factors with specificity of self-reported uterine fibroid status among 1767 RFTS and 362 UFS participants with no fibroids detected at study ultrasound. Specificity ratios are specificity of self-report in subgroup of interest compared to specificity in the reference group. UFS specificity ratios are adjusted for parity, and (for unstratified estimates) race/ethnicity. RFTS estimates are unadjusted. ^aAmong women with a previous pregnancy. ^bEstimates obtained using Poisson regression.