Popular injectable contraceptive increases risk of STD's

The injectable contraceptive depot-medroxyprogesterone acetate (DMPA) appears to increase a woman’s risk of acquiring the sexually transmitted infections chlamydia and gonorrhea by approximately three fold when compared to women not using a hormonal contraceptive, according to a study jointly funded by the National Institute of Child Health and Human Development and the U.S. Agency for International Development’s Office of Population and Reproductive Health.

DMPA is marketed under the product name Depo Provera and is an injection (a shot) that protects against pregnancy for three months.

The study was unable to determine why DMPA might increase the risk for these infections.

The injection contains a synthetic hormone called progestin. This chemical is similar to the natural hormone progesterone that is produced by the ovaries during the second half of the menstrual cycle. Progestin prevents pregnancy by:

  1. Changing the lining of the uterus making it less likely for implantation (or less likely for pregnancy to occur). Thickening cervical mucus making it harder for sperm to enter the uterus.

  2. Stopping the eggs from being released from the ovaries.

“These findings underscore the need to counsel all sexually active women who use DMPA and who are not in a mutually monogamous relationship to use condoms consistently and correctly,” said the study’s first author, Charles Morrison, Ph.D., of Family Health International in Research Triangle Park, North Carolina. “For sexually active women not in a mutually monogamous relationship, limiting the number of partners may also help to reduce the risk.”

The study appears in the September Sexually Transmitted Diseases.

The researchers also tested another type of contraceptive formulation, oral contraceptives containing both estrogen and progestin. The researchers concluded that oral contraceptives do not appear to significantly increase the risk of chlamydial infection and gonorrhea.

To conduct the study, the researchers recruited women from two Baltimore, Maryland area clinics. One clinic was within the city of Baltimore and served a predominantly African American clientele. The other was in the Baltimore suburb of Towson and predominantly served white, college-age women. The women chose whether they wanted to use DMPA, oral contraceptives, or a non-hormonal contraceptive method.

Of the 819 women included in the study’s final analysis, 77 percent were single, 75 percent had never given birth, and 79 percent were high school graduates. Roughly 52 percent were white, 43 percent were African American, and the remaining women were of other racial or ethnic origins. Study participants ranged in age from 15 to 45 years. After enrolling in the study, they were tested for chlamydial and gonococcal infection after three, six, and 12 months.

The study compared three groups of women, those starting oral contraceptives, those starting DMPA injections, and those women who did not use hormonal contraceptives. By the time the study had ended, 45 women had developed either a chlamydial or gonococcal infection. The researchers estimated that women using DMPA had approximately 3½ times the risk of developing a chlamydia or gonorrhea infection than did women who were not using a hormonal contraceptive.

The study was designed to examine the combined number of cases of chlamydial and gonococcal infection and was not large enough to calculate the risk for acquiring each infection separately, says the study’s project officer, Joanne Luoto, M.D., of NICHD’s Contraception and Reproductive Health Branch. The study was unable to identify the means by which DMPA might increase the risk for chlamydial or gonococcal infection.

Other authors of the study are at the University of North Carolina at Chapel Hill; at Johns Hopkins University in Baltimore, Maryland; and at Planned Parenthood of Maryland in Baltimore.

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