Letter: Progestagen-only contraception and tubal pregnancies.
D000328:Adult; D003276:Contraceptives, Oral / Q000009:adverse effects*; D005260:Female; D006801:Humans; D009640:Norethindrone / Q000008:administration & dosage / Q000009:adverse effects*; D011247:Pregnancy; D011274:Pregnancy, Tubal / Q000139:chemically induced*
D003276:Contraceptives, Oral; D009640:Norethindrone