Sexual activity

Sexual activity
By Sandy Hemphill, Contributing Writer, BabyMed

Women hoping to become pregnant know conception is most likely to occur during the most fertile phase of the menstrual cycle. Fertility is highest at in the days leading up to ovulation so sexual activity is encouraged at this time especially but new research indicates intercourse throughout the menstrual cycle promotes conception, too.

The new research from Indiana University (IU) explains how the immune system encourages pregnancy when a woman’s sex life is lively and includes intercourse at all phases of the menstrual cycle. The findings of the study, led by Tierney Lorenz of the university’s Kinsey Institute for Research in Sex, Gender, and Reproduction, are thought to be the first documented evidence that the immune system responds to social behavior and not just to external threats as has been previously understood.

Conception and pregnancy present a “tricky dilemma” to the immune system, according to Lorenz. The immune system’s response to outside invaders such as a virus or bacterium keeps us healthy but sperm, embryo, and fetus all carry foreign DNA, too. If the immune response remained the same all the time to all foreign invasions, it would fend off all elements with DNA that differs from the woman’s and make conception impossible.

Lorenz and her research team enlisted 30 healthy women of childbearing age for their examination of immune response to the menstrual cycle:

  • 14 study participants were sexually active
  • 16 were sexually abstinent

None of the study participants were pregnant or taking medications that affect the hormonal or immune systems. Each one provided a saliva sample taken at four strategic phases of the menstrual cycle:

  • Menstrual
  • Follicular (between menstruation and ovulation)
  • Ovulatory
  • Luteal (between ovulation and menstruation)

When a foreign invader is detected in the bloodstream, helper T cells signal white blood cells to produce antibodies (immunoglobulins) to fend off illness. Of particular interest to the IU study were two types of helper T cells and two types of immunoglobulin antibodies:

  1. Type 1 helper T cells — defend the body against external threat.
  2. Type 2 helper T cells — alert the immune system that sperm, embryo, and fetus are desired foreign invaders that should not be destroyed.
  1. Immunoglobulin A antibodies — exist only in the mucus secretions of the female reproductive tract and respond to sperm and pregnancy.
  2. Immunoglobulin G antibodies — fight foreign DNA in the bloodstream for all the body except the uterus.

Examination of the saliva samples revealed immune system changes during the follicular and luteal phases of women who enjoy an active sex life:

Follicular (pre-ovulation phase during which follicles in the ovaries are maturing for release as an egg):

  • Type 1 helper T cells were found in high concentration.
  • Immunoglobulin A was also in high concentration.

Luteal (after ovulation when uterine lining thickens in anticipation of pregnancy):

  • Type 2 helper T cells were in significantly higher concentration.
  • Immunoglobulin G was also in highest concentration.

These immune-system fluctuations did not occur in the women who were abstaining from sexual intercourse.

The IU findings may prove beneficial to couples seeking treatment for infertility but may also prove helpful in treating sexually active women who have autoimmune disorders.


  1. "Indiana University study: Sexual activity causes immune system changes that increase chances of conception." EurekAlert! Indiana University, 4 Oct. 2015. Web. 10 Nov. 2015.
  2. Lorenz, Tierney K., Julia R. Heiman, and Gregory E. Dumas. "Sexual activity modulates shifts in TH1/TH2 cytokine profile across the menstrual cycle: an observational study." Fertility and Sterility (2015). Elsevier Inc.. Web. 10 Nov. 2015.