RT Journal Article SR Electronic T1 Contraception—Natural Family Planning JF The Journal of the American Board of Family Practice JO J Am Board Fam Med FD American Board of Family Medicine SP 278 OP 279 DO 10.3122/jabfm.4.4.278 VO 4 IS 4 A1 Woolley, Robert J. YR 1991 UL http://www.jabfm.org/content/4/4/278.abstract AB