Sentence:  Pope Pius 12 , declared in 1951 that it is possible to be <WSD>exempt</WSD> from the normal obligation of parenthood for a long time and even for the whole duration of married life , if there are serious reasons , such as those often mentioned in the so-called medical , eugenic , economic and social `` indications '' . 
Meaning of the word marked with <WSD> tags:  (of persons) freed from or not subject to an obligation or liability (as e.g. taxes) to which others or other things are subject