Murray ..... My history on this is somewhat vague but I watched a TV documentary about it some years ago.
Apparently members of the medical profession were becoming concerned about the number of "mentally retarded" people being admitted to mental institutions ( these included young girls who became pregnant without being married, or who were otherwise deemed to be out of their parents control and people of no fixed abode) so with the agreement of their governments (I know GB and Germany were involved along with certain other European countries) they started a programme of compulsory sterilisation.