Originating from the Soviet Union, the psychoprophylactic method known as painless childbirth spreads in Western Europe from the beginning of the 1950s. This article aims to show that this type of non-pharmacological analgesia represents only a partial innovation with respect to practices already used locally. It exercises a power of attraction less as an innovative tool capable of resolving an identified medical problem than as a demonstration of scientific progress. A systematic chronology of the stages of its implementation in France and in Switzerland shows that it actually takes hold in the medical communities of those two countries thanks to a support campaign organised by communist circles. Without a clearly partisan media campaign that aroused a keen interest on the part of the general public, its intrinsic value would not singlehandedly have afforded it such a broad (national and international) dissemination. Its political connections – that may have been expected to lead to its rejection – did not diminish its appeal to the professional interests of obstetricians, to their pragmatic approach and to their representations of women; moreover it carried the aura of Ivan Pavlov’s scientific fame. Painless childbirth thus provides a remarkable example of the social contingency and political heteronomy of scientific and medical knowledge.