Effectiveness of contraception in Belgium: results of the Second National Fertility Survey, 1971 (Nego ii).
D000328:Adult; D001530:Belgium; D003267:Contraception / Q000379:methods; D005069:Evaluation Studies as Topic; D005191:Family Characteristics; D005193:Family Planning Services; D005260:Female; D006801:Humans; D011247:Pregnancy; D013997:Time Factors