“The FRT (female reproductive tract) is tremendously complex,” according to Charles R. Wira, a research scientist who has just published the findings of a study that explores how the menstrual cycle affects a woman’s risk of sexually transmitted disease (STD). His research reveals a woman’s risk of STD infection is in sync with her menstrual cycle and it’s all about making it easier for a successful pregnancy to occur.

Wira and his research colleagues at Dartmouth College’s Geisel School of Medicine in Hanover, New Hampshire, discovered a “window of vulnerability” to STD infection (also STI, sexually transmitted infection). This finding is considered so significant by Wira’s colleagues that it is being referred to as “a sea change” for research involving female reproduction.

The body’s immune system is regulated by hormones, including estradiol and progesterone, two sex hormones that are strategically secreted during the second half of the menstrual cycle, when conception is most likely to occur. Estradiol production triggers ovulation and progesterone production. Together, they stimulate the uterus to prepare for implantation of a fertilized egg and promote the health of pregnancy.

The effect of estradiol and progesterone on the woman’s immune system is to suppress it so pregnancy can occur. If a woman is exposed to a virus or other pathogen that causes infection at this strategic time of the menstrual cycle, her risk of infection increases since her immune system is momentarily weakened to encourage pregnancy.

Researcher Marta Rodriguez-Garcia said the benefits of the team’s findings apply to a number of issues that affect female reproduction: infertility, cancers involving the FRT, human papilloma virus (HPV) infection, and the spread of STIs that include HIV/AIDS, chlamydia, genital herpes, gonorrhea, and syphilis. Data from the Centers for Disease Control and Prevention (CDC) indicate as many as 19 million new STIs occur each year, with almost half of them occurring in people 15 to 24 years of age. Women are usually affected by an STI more severely than men.

The Dartmouth study offers hope that new treatment options can be developed that take advantage of this newly discovered window of vulnerability. Other benefits may include:

  • Behavioral Changes — Women at risk of STI may be counseled to avoid sexual activities during this riskiest time of the month.
  • Drug Therapies — Vaccines and microbicides could someday be formulated to take advantage of the menstrual cycle’s effect on the immune system.
  • Contraception — Potential development of chemical contraceptives that also protect against HIV infection.

Symptoms of many STIs are easily mistaken for more minor medical conditions that are often ignored. Some STIs produce symptoms so minor they sometimes go unnoticed. According to the CDC, 24,000 women each year are rendered infertile due to an untreated STD infection. Infant death occurs about 40% of the time when a woman is pregnant with untreated syphilis.


  1. Wira, Charles R., Marta Rodriguez-Garcia, and Mickey V. Patel. "The role of sex hormones in immune protection of the female reproductive tract." Nature Reviews / Immunology 15 (2015): 217-30. Nature Publishing Group. Web. 26 Mar. 2015.
  2. "10 Ways STDs Impact Women Differently from Men." CDC Fact Sheet. Centers for Disease Control and Prevention, Apr. Web. 26 Mar. 2015.
  3. "Sexually transmitted infections (STI) fact sheet." WomensHealth.gov. US Department of Health and Human Services, 16 July 2012. Web. 26 Mar. 2015.