Sentence:  With the exception of the Roman Catholic and the Orthodox Catholic Churches , most churches make no moral distinction between <WSD>rhythm</WSD> and mechanical or chemical contraceptives , allowing the couple free choice . 
Meaning of the word marked with <WSD> tags:  natural family planning in which ovulation is assumed to occur 14 days before the onset of a period (the fertile period would be assumed to extend from day 10 through day 18 of her cycle)