The Black Women’s Health Study is an ongoing prospective cohort study that was established in 1995, when approximately 59,000 black women in the United States aged 21–69 years were enrolled through self-administered questionnaires mailed to subscribers of Essence
magazine, members of black professional organizations, and friends and relatives of early respondents.11
The baseline questionnaire elicited information on demographic and behavioral characteristics, health care use, and medical conditions. On the 1997 questionnaire, participants were asked “what is your race?” and to select all that applied from the following categories: “black,” “white,” “Asian or Pacific Islander,” or “American Indian or Alaskan Native.” Those who selected “black,” regardless of any other group selected, were retained in the cohort. Six percent of the sample was foreign-born (54% Caribbean, 7% Africa, 39% South or North America/Europe/Asia/other), and less than 2% reported Hispanic ethnicity. The cohort is followed every 2 years by postal questionnaire, and more than 80% of the original cohort has completed a questionnaire in each follow-up cycle. Respondents in the Black Women’s Health Study represent various geographic regions of the United States, with most residing in California, New York, Illinois, Michigan, Georgia, and New Jersey. The study protocol was approved by the institutional review boards of Boston University Medical Center and Howard University Cancer Center.
Follow-up for the present analysis began in 1997, the start of the second questionnaire cycle, because self-reported method of confirmation for uterine leiomyoma was first elicited on the 1999 questionnaire. Of the 53,279 women who completed the 1997 questionnaire, we restricted the sample to premenopausal women because uterine leiomyomata are rare after menopause.12
We therefore excluded women who reported natural menopause (n = 5,143), hysterectomy (n = 6,625), bilateral oophorectomy (n = 4,175), medication-induced menopause (n = 218), or unknown menopausal status (n = 522). We further excluded women who reported a diagnosis of uterine leiomyomata before 1997 (n = 10,450), who reported the condition without information on year of diagnosis (n = 99) or method of confirmation (n = 208), who did not complete a follow-up questionnaire (n = 2,193), or who had missing data on key stratification variables (n = 751). The remaining 22,895 women were followed for incidence of uterine leiomyomata during the subsequent 4-year period. The small proportion of women who were lost to follow-up or who had incomplete covariate data had lower educational attainment than respondents but were similar with respect to age, parity, body mass index, and other risk factors for uterine leiomyomata.
On the 1999 and 2001 follow-up questionnaires, women were asked whether they had been diagnosed with “fibroids in uterus” in the previous 2-year interval, the calendar year in which they were first diagnosed, and whether their diagnosis was confirmed by “pelvic exam” and/or by “ultrasound/hysterectomy.” Among cases reporting confirmation by “ultrasound/hysterectomy,” a diagnosis was considered “hysterectomy-confirmed” if the woman reported hysterectomy on the same questionnaire and “ultrasonography-confirmed” otherwise. A diagnosis was considered “confirmed by pelvic examination” if only that method was reported.
Incident cases were defined as women who self-reported a first diagnosis of leiomyomata that was confirmed by pelvic examination, ultrasonography, or hysterectomy. In the present study, “incident” refers to the initial diagnosis rather than the true onset of uterine leiomyomata, which could differ by an extended time period if tumors were present before they became palpable or symptomatic.12
The diagnosis of uterine leiomyoma often is suspected when an enlarged irregular uterine contour is palpable on pelvic examination. Ultrasonography is the standard used to confirm diagnoses.12
Ultrasonography has high sensitivity (99%) and specificity (91%) relative to histologic evidence.13,14
Because histologically confirmed cases represent only 10–30% of cases for whom ultrasonography evidence is available and studies restricted to histologically confirmed cases may spuriously identify risk factors associated with large tumor size, symptoms, or treatment preference,15
we examined all 3 methods of confirmation. For comparisons of peak age at diagnosis across studies, however, we restricted our case group to cases confirmed by ultrasonography or hysterectomy because diagnoses confirmed only by pelvic examination may represent other pathology.13
This definition also was used by the Nurses’ Health Study II, a prospective study with similar methodology to the Black Women’s Health Study.3
We assessed the accuracy of self-report in a random sample of 248 ultrasonography- or hysterectomy-confirmed cases. These cases were mailed supplemental surveys regarding their initial date of diagnosis, method of confirmation, symptoms, and treatment, and they were asked for permission to review their medical records. We obtained medical records from 126 of the 128 women who gave us permission and verified the self-report by medical record in 121 (96%). Among the 188 (76%) cases who completed the supplemental survey, 71% reported leiomyoma-related symptoms before being diagnosed with the condition. This proportion was higher among hysterectomy-confirmed cases (79%). When cases were asked how their diagnosis came to clinical attention, 55% of cases reported they were diagnosed because they sought medical care for leiomyoma-related symptoms; 32% were diagnosed during a routine pelvic examination, and the remaining 13% were diagnosed while receiving care for some other condition (with more than 85% citing “pregnancy” as the other condition).
No statistically significant differences were observed between cases who did and did not release their medical records with respect to important demographic and lifestyle factors (age, body mass index, education, oral contraceptive use, recency of Pap test, and health insurance coverage: χ2 test P > .2); self-reported method of confirmation (64% ultrasound examination compared with 71% hysterectomy, P = .55); the report of symptoms before the initial diagnosis (73% compared with 66%, P = .31); the type of presenting symptoms (menorrhagia: 56% compared with 47% [P = .28]; pelvic pain: 48% compared with 42% [P = .47]; frequent urination: 21% compared with 25% [P = .53]; infertility: 10% compared with 12% [P = .89]); or how initial diagnosis was made (sought care for leiomyoma-related symptoms: 57% compared with 46% [P = .18]; diagnosed during a routine pelvic examination: 31% compared with 34% [P = .64]; diagnosed while receiving care for another condition: 10% compared with 14% [P = .42]). Therefore, the cases who released their medical records appeared to be representative of the larger case group.
Woman-years at risk were calculated from the start of follow-up (March 1997) until the diagnosis of uterine leiomyomata, menopause, death, loss to follow-up, or end of follow-up (March 2001), whichever came first. Age was updated at the start of each questionnaire cycle. Incidence rates for each age category were computed as the number of incident cases divided by the woman-years accumulated. Poisson regression16
was used to estimate overall and age-specific incidence rates and 95% confidence intervals (95% CIs) for self-reported uterine leiomyomata confirmed by pelvic examination, ultrasonography, or hysterectomy. Analyses were repeated within strata of education (≤12, 13–16, 17 + years), oral contraceptive use (current compared with never), cigarette smoking (current, former, never), body mass index (< 25, 25–29, 30+ kg/m2
), and geographic region of residence (West, Midwest, South, Northeast). All analyses were conducted using SAS statistical software (SAS Institute, Cary, NC).