Inserting a foreign device into the uterus causes an inflammatory response, which creates a hostile environment for sperm.
[3][4] The silver wire used to construct later versions of Gräfenberg's ring was contaminated with copper, which increases this spermicidal effect.
[1] In 1934, Japanese physician Tenrei Ōta developed a variation of the Gräfenberg ring that contained a supportive structure in the center.
[5] Furthermore, their use and development was stifled by World War II politics: contraception was forbidden in both Nazi Germany and Axis-allied Japan.
The rest of the Western world did not learn of the work of Gräfenberg and Ota until well after the war ended.