Natural family planning and Rhythm method

Natural family planning noun - Any of several methods of family planning that do not involve sterilization or contraceptive devices or drugs; coitus is avoided during the fertile time of a woman's menstrual cycle.

Rhythm method and natural family planning are semantically related. In some cases you can replace phrase "Rhythm method" with "Natural family planning", this phrases are similar.

Rhythm method noun - 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).

Natural family planning and rhythm method are semantically related. Sometimes you can use "Natural family planning" instead a noun phrase "Rhythm method".