Objective
We sought to compare sexual function and hormone concentrations in combined oral contraceptive (COC) and injectable progestin users.
Study Design
Sexually active COC and depot medroxyprogesterone acetate (DMPA) users completed the Female Sexual Function Index (FSFI) questionnaire, a demographic data form, and had serum testosterone and estradiol levels measured. Multiple linear regression was used to measure associations of interest.
Results
Among 50 subjects enrolled, COC users had lower levels of free testosterone compared to DMPA users (0.2 vs 0.6 pg/mL; P < .0001) and higher levels of estradiol (75.8 vs 62.8 pg/mL; P = .0057), but scores of desire (4.2 vs 3.8; P = .27), scores of arousal (5.0 vs 4.8; P = .46), or total scores (30.1 vs 28.8; P = .28) were no different. Demographic characteristics were similar except for ethnicity, level of education, gravidity, parity, and frequency of intercourse. In multivariate analysis, birth control type was not significantly associated with desire score or total FSFI score.
Conclusion
While users of COC and DMPA have significantly different sex hormone levels, they are not different in sexual function as measured by the FSFI.
Since the introduction of hormonal contraception, there have been reports that oral contraceptives may interfere with sexual desire. While reviews of this literature conclude that decreased libido resulting from hormonal contraception affects only a minority of contraceptive users, such reports may lead to noncompliance or discontinuation of effective contraception.
A commonly suggested rationale for this effect is the decrease in bioavailable testosterone caused by combined oral contraceptives (COCs). Testosterone is acknowledged to be the primary sex steroid influencing desire in women. The estrogen in COCs increases serum concentrations of sex hormone–binding globulin, which binds testosterone and yields less bioavailable forms of this hormone. Whether this reduction in free testosterone can adversely influence libido in some women remains controversial. Although some studies show no correlation between androgen levels and sexual function in COC users, other recent studies suggest that the decrease in free testosterone contributes to dysfunction. A panel of experts in a consensus statement about female androgen insufficiency cite the low androgen state caused by COCs as a possible source of clinical symptoms including sexual dysfunction.
Depot medroxyprogesterone acetate (DMPA) injection is another form of hormonal contraception commonly used by women. Because this form of contraception contains no estrogen, it is thought to have less of an effect on sex hormone–binding globulin, and therefore less effect on free testosterone. While this may translate into less of an effect on sexual desire, there have been few studies that examine sexual functioning in women using this contraceptive. Although 1 prospective analysis of women commencing contraception in China demonstrated no difference in sexual functioning from baseline to 4 months in women using DMPA, another survey of adolescents using DMPA identified a 15% rate of decreased libido. There have been no studies, however, comparing sexual function between users of COCs and injectable progestins as it relates to differences in serum hormone concentrations.
This study examines sexual functioning in DMPA users compared with COC users. By measuring androgen and estrogen levels in these women, we also explored the correlation between hormone levels and sexual desire. We hypothesized that women using injectable progesterone would have higher levels of free testosterone, and fewer reports of decreased sexual desire. In addition, other domains of sexual function were examined for correlation with hormonal differences between the 2 groups.
Materials and Methods
Women presenting for a routine annual or follow-up contraceptive visit were approached for enrollment in the study. Women were eligible for the study if they were sexually active (defined as engaging in regular sexual encounters with an available partner), on the same hormonal contraceptive regimen for at least 6 months, and being prescribed contraception only for pregnancy prevention and not for any other medical or gynecological indication. Women were excluded from participation if they were younger than 18 years, presenting with a gynecological or medical symptom, or seeking to change their method of contraception. Women with active psychiatric disease or who were taking any psychoactive medication were also excluded.
Following informed consent, each subject was asked to fill out a brief demographic and sex history questionnaire that also solicited opinions on amount of monthly bleeding, level of satisfaction with contraception, satisfaction with relationship, and level of life stress. Satisfaction was scored using a 5-point Likert scale with 5 indicating high satisfaction. Life stress was also assessed by a 5-point Likert scale with 5 indicating high average daily stress level. Subjects also completed the Female Sexual Function Index (FSFI), a brief, validated questionnaire designed to assess domains of sexual functioning in clinical trials. Each domain is scored individually with a score of 6 indicating maximum function for that area; the total score represents the total of the 6 domains with 36 being the maximum score.
Venipuncture was then performed to measure serum levels of total testosterone, free testosterone, and estradiol. Both testosterone and estradiol levels were assayed by a chemiluminescent immunological reaction performed by the Advia Centaur XP (Siemens Corp, Munich, Germany). The assay detects estradiol with a sensitivity of 7.0 pg/mL and a coefficient of variance up to 12%. It detects testosterone with a sensitivity of 10 ng/dL and a coefficient of variance up to 7%. Free testosterone was measured using the Coat-a-Count radioimmunoassay (Diagnostic Products Corp, Los Angeles, CA). The coefficient of variance for this assay is up to 26% for small concentrations.
Total FSFI scores and individual domain scores were compared between oral contraceptive users and DMPA users by Wilcoxon sum rank tests. Correlation indices were calculated to examine the relationship between serum hormone values and FSFI scores. Demographic variables were compared between the 2 groups to elicit confounding factors, with t tests used for continuous variables and Fisher’s exact test for categorical variables. A linear regression model was constructed to control for confounding differences between the groups.
A previous survey of healthy women without sexual symptoms described an average total FSFI score of 31.2, and a desire domain score of 4.0. A total score of 26.55, however, is clinically associated with sexual dysfunction. To demonstrate a difference of 5 points in the total FSFI score, or 1 point in the desire domain, at a significance level of .05 at a power of 80%, power analysis revealed that 25 subjects would need to be enrolled in each group. The protocol was approved by the Biomedical Science Institutional Review Board of the Ohio State University.
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