Objective
The objective of the study was to determine the prevalence and characteristics of vulvodynia among women in southeast Michigan.
Study design
A population-based study of adult women was conducted, using telephone recruitment and completion of a self-administered survey. Weighted estimates of vulvodynia prevalence and characteristics were determined.
Results
Over a year, 2542 women were recruited and 2269 (89.3%) completed the self-administered survey. The weighted prevalence of vulvodynia was 8.3% (95% confidence interval, 7.0–9.8) or approximately 101,000 women in the targeted population. Prevalence remained stable through age 70 years and declined thereafter. Among sexually active women, the prevalence was similar at all ages. Of 208 women meeting vulvodynia criteria, 101 (48.6%) had sought treatment, and only 3 (1.4%) had been diagnosed with vulvodynia (unweighted values). Previous vulvodynia symptoms had resolved in 384 women (16.9%) after a mean duration of 12.5 years.
Conclusion
Vulvodynia is common, although rarely diagnosed. Prevalence remains high among sexually active women of any age.
Vulvodynia is a chronic pain condition associated with local hypersensitivity of the vulva that may be provoked (eg, intercourse or tampon use), unprovoked (spontaneous), or both. Although previously thought to be rare, chronic, and more common among white women, recent studies suggest that vulvodynia may occur in 3-14% of women of all ethnicities and may resolve in a substantial proportion of women. Nonetheless, the majority of women with vulvar pain remain undiagnosed and inadequately treated. The recent availability of a validated instrument to screen for vulvodynia based on survey responses allows women likely to have vulvodynia to be identified in the general population.
We conducted a population-based study of women in a 4-county area of southeastern Michigan to evaluate the prevalence of current and past vulvodynia and to assess the demographic and pain characteristics of those with and without this syndrome.
Materials and Methods
The study was approved by the Institutional Review Board of the University of Michigan School of Medicine.
Study population
We recruited a random sample of 2542 women, representative of women in a 4-county area in southeastern Michigan, using random digit dialing (RDD). In collaboration with the Survey Research Operations at the Institute for Social Research at the University of Michigan, we recruited women by calling landline telephone numbers purchased from Genesys, an RDD telephone frame vendor. When a household was reached and a woman aged 18 years or older lived in that household, the number of women and their ages were elicited. For households with more than 1 eligible woman, 1 woman was randomly designated as a potential participant. Eligible women were invited to participate in a study on women’s health that would involve a brief telephone-screening interview to complete enrollment, an online or written survey within 2 weeks of enrollment, and a follow-up survey every 6 months for 3 years. After giving informed consent, women were enrolled in the longitudinal study.
The sampling strategy was designed to reflect the distribution of age and country of residence of women in the 4-county area as indicated by the 2000 census. To ensure that our sample would appropriately represent this distribution, the age eligibility of potential additional participants was adjusted as enrollment proceeded. Hence, after 3 months, the age criterion was limited to age 18-60 years and at 9 months to age 18-39 years. Following recruitment of 2505 women using landline numbers, an additional recruitment effort using cell phone numbers from the same area was implemented to access and increase the representation of women aged 18-29 years who did not have landline telephones. Cell phone recruitment was similar to landline recruitment, with modifications made consistent with cell phone safety (eg, assuring the respondent was in a safe place to talk), and an additional 37 women were recruited. The number of landline telephones and cell phones accessed for personal use was determined for weighting purposes.
Informed consent information was given at the time of the telephone recruitment and again in the survey cover letter and subsequent completion of the telephone interview and the survey implied consent. We sent each participant a letter introducing the survey with the initial $5 stipend, an enclosed survey, and a postage-paid return envelope or with the web address to access the online survey. A reminder letter or email was sent 2 weeks later, and survey reminder calls were made if no survey had been received after another 2 weeks. Every 6 months, follow-up surveys are being sent over a 3 year period. This article focuses on the initial baseline survey data.
Survey instrument
The baseline questionnaire obtained information about the presence or absence of vulvar pain, the characteristics of this pain, and information about the women’s demographic characteristics and reproductive health history. The survey instrument included previously validated questions that have been found to predict vulvodynia case status with substantial accuracy.
Diagnostic criteria
The clinical status of each participant was categorized as a current vulvodynia case, a past vulvodynia case, having dyspareunia not consistent with vulvodynia, or a control without dyspareunia or vulvar pain. The diagnostic criteria for vulvodynia were based on our previously validated survey-based criteria. A screening-based diagnosis of vulvodynia depended on having pain at the vulva or opening to the vagina that had been present for a minimum of 3 months, without resolution. Past cases were those whose history indicated they had had the vulvar pain lasting at least 3 months at some point in their life that had resolved. The diagnosis of dyspareunia was applied to women reporting pain with intercourse who did not meet criteria for vulvodynia based on location or duration. Controls included women who reported no current pain with intercourse and no vulvar pain. Because women not having intercourse may be unaware of their vulvar sensitivity, control women were subdivided into 2 categories: strict controls (asymptomatic, who had had intercourse within 6 months) and controls with no intercourse (asymptomatic but had not had intercourse within 6 months).
Statistical analysis
Because a complex sampling design was used for data collection, we carried out a weighted analysis using the SPSS Complex Samples module (IBM PASW Statistics 18; SPSS Inc, Chicago, IL). Details are given in the Appendix . In brief, the analyses were weighted for the probability of selection, nonresponse, and poststratification alignment to the age and county population subgroups.
The sampling weights accounted for the probability of selection based on the number of telephone numbers selected vs the number available in the 4-county area, the number of unique telephone numbers in each respondent’s household, and the probability of within-household selection. In addition, nonresponse weights were created using a propensity score approach that was based on age, education, and ethnicity (factors associated with both likelihood of response and the vulvodynia case status). Poststratification weights ensured that our sample properly represented the age cohorts (in 10 year categories) in each of the 4 counties in the 2000 census data. All analyses used the weighted data.
The prevalence and 95% confidence intervals of vulvodynia were calculated for the total population and for each demographic subgroup. Demographic characteristics of vulvodynia cases vs all noncases as well as vs controls were compared and prevalence odds ratios and their 95% confidence intervals calculated. Multivariable logistic regression was used to assess the association of demographic characteristics with the case status.
Results
Between September 2008 and November 2009, 2542 women were recruited to the study (2505 via landline telephones and 37 via cell phones). Details of sampling and enrollment characteristics are provided in the Appendix . In brief, 66% of the working landline numbers were reached, and of these, 64% had an eligible woman in the household. A total of 79% of the eligible landline respondents completed the telephone-screening interview and were enrolled in the longitudinal study. In the cell phone recruitment, the proportion of working lines that identified an eligible female based on sex, age, and geographic location was substantially lower (16%), primarily because of reaching voice mail, male respondents, or younger women. However, once an eligible woman was identified, the screening completion rate of the cell phone recruitment was similar (76%) to that of the landline recruitment ( P = .55).
Of 2542 women enrolled, 21.4% (544) were aged 65 years and older, compared with 23.0% of women in the 4-county census ( P = .06). Our sample approximated the ethnicities of the 4-county population, with 20.3% black (n = 515) and 73.5% white (n = 1869), compared with 25.7% and 68.3%, respectively, in the population. In both our study sample and the 4-county population, 2.8% described themselves as Hispanic.
Of the 89.3% who completed their baseline survey (2269), 44.4% used the paper format and 55.6% completed it online. Compared with noncompleters, women completing the baseline survey were younger (50.4 ± 16.7 years vs 54.2 ± 19.2 years, P = .002), more likely to be white (76.0% vs 53.1%, P < .001), and more highly educated (4.8% vs 11.4% did not complete high school, P < .001).
In a multivariable analysis, age, education, and ethnicity remained statistically associated with survey completion. Completers and noncompleters did not differ in lifetime history of pain with intercourse or in reporting having past or current vulvar pain.
Within this 4-county area, there are approximately 1.4 million women aged 18 years or older. The unweighted prevalence of vulvodynia by our screen was 9.2%, and the weighted prevalence was 8.3% (95% confidence interval [CI], 7.0–9.8) ( Table 1 ). Another 17.9% of women reported symptoms suggestive of past vulvodynia. Based on the weighted analysis, 101,007 women in the 4-county area are estimated to have vulvar pain consistent with vulvodynia, with another 218,219 having a history of such pain that has since resolved.
