Heat-based contraception

The deleterious effect of hyperthermia on male fertility has been known since ancient times. But it is from the 19th century onwards that the scientific community started to carry out research to better understand the phenomenon.

In the 1930s, physician Marthe Voegeli[6] explored the role of heat in male sterilization. She conducted experiments on the relationship between heat and spermatogenesis. She found that exposing the testicles to high temperatures in hot baths altered fertility. Sperm concentrations in the volunteers decreased so much so that they were considered infertile. She was the first scientist to popularize this alternative method of contraception for men.

The thermal dependence of spermatogenesis was confirmed in various studies carried out between 1950 and 1970 by Doctors Watanabe and Robinson.[7][8][9]

The effect of temperature was first studied with external processes such as hot baths or saunas with temperatures above 40 °C over short periods of exposure.[10][11]

A history of testicular descent problems (cryptorchidism) or professional practices that lead to elevated scrotal temperature and even fever are identified as factors that are prone to reduce fertility.[12] Studies have been carried out with daily exposure of the testicles to less intense heat, around 37 °C, a temperature that is close to that of the body.[13][14] A contraceptive device using body heat was patented by Schopp Andreas in 1999.[15]

The production of sperm can be disrupted with a rise in temperature.[16]

Thermal methods involve heating the testicles so that sperm production is slowed down. The spermatozoa are thus produced at a slightly lower temperature than that of the body, 1 to 2 °C below 37 °C.

The cremaster muscle covers the testicles. It works involuntarily. Its role is to bring the testicles down if the body temperature rises or to raise them if the body temperature drops. This process allows it to regulate the temperature of the testicles and to keep it several degrees lower than that of the body in order to enable an ideal spermatogenesis.[17][18]

Other effects have also been observed, such as a decrease in motility and an alteration in the morphological characteristics of the spermatozoa that are produced.[18][19][20][21]

Some suggest that exposure to high temperatures (47 °C) can affect fertility for months.[3]

Thermal methods do not cause azoospermia, but a reduction of the spermatozoa[22] below the contraceptive threshold considered to be effective.

This contraceptive threshold was defined in 2007 for male thermal, chemical and hormonal contraception methods. It corresponds to 1 million spermatozoa per milliliter per ejaculate.[23][24][25]

The only method that has been tested on enough volunteers to establish that the effectiveness of thermal male contraception is satisfactory is the artificial cryptorchidism method with testicular ascent using a specific device. During the clinical studies, 50 couples were followed over 537 cycles of pregnancy. Only one resulted in a pregnancy due to a misuse of the technique. The Pearl Index would therefore be less than 0.5 and this contraception method can be considered effective according to the standards of the World Health Organisation (WHO).

The maximum limit of exposure to heat is around 45 °C, which causes the coagulation of intracellular proteins on living cells. However, exposure above 41 °C for short periods of time may be used, as has been the case for scientific studies on the effect of hot baths.[26]

In the case of artificial cryptorchidism or thermal insulation of the testicles, the use of a temperature close to that of the body (37 °C)  has made it possible to increase the time of exposure in order to slow down the spermatogenesis process over longer periods, 4 years in a row at most. To date, only a decrease in testicular volume by a few percents has been observed during the contraceptive period. There is no evidence of an increased risk of testicular torsion. However, it has been shown that the nuclear quality of the spermatozoa was altered during the phase of inhibition of the spermatogenesis, but that this was reversible 3 months after the subject stops practicing artificial cryptorchidism.[27] This finding should be taken into account when using this contraception method, during the inhibition phase and for 3 months after treatment discontinuation.[24]

• Male contraceptive
• Artificial cryptorchidism
• Marthe Voegeli
• Birth control
• Comparison of birth control methods
• Human population planning
• Masculinity

• From linked International Male Contraception Coalition and Male Contraception Information Project:
  • "External heat". International Male Contraception Coalition. Retrieved 2008-06-21.
  • "Suspensories / Internal heat". International Male Contraception Coalition. Retrieved 2008-06-21.
  • "Heat Methods of Male Contraception". Frontiers in nonhormonal male contraception. Male Contraception Information Project. Archived from the original on 2013-05-14. Retrieved 2008-06-21.
• Jenks, C (2006). "Experimental Method of Male Contraception". Retrieved 2008-06-21. – a toxicologist's account of successful experiments on himself with suspensory briefs, also provides excerpts from some research papers
• Asaravala, A (2004-12-04). "Laptops a Hot Fertility Issue". Wired.