Inserting a foreign device into the uterus causes an inflammatory response, which creates a hostile environment for sperm. The silver wire used to construct later versions of Gräfenberg's ring was contaminated with copper, which increases this spermicidal effect.
In 1934, Japanese physician Tenrei Ota developed a variation of the Gräfenberg ring that contained a supportive structure in the center. The addition of this central disc lowered the IUD's expulsion rate. However, insertion of these devices caused high rates of infection and were condemned by the medical community. Furthermore, their use and development was stifled by World War II politics: contraception was forbidden in both Nazi Germany and Axis-allied Japan. The Western world did not learn of the work by Gräfenberg and Ota until well after the war ended.