Secular movements in dizygotic twinning rates and in sperm counts.
James
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D003276:Contraceptives, Oral; D005060:Europe; D005260:Female; D049673:History, 20th Century; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000706:statistics & numerical data; D013076:Sperm Count; D014429:Twins, Dizygotic / Q000266:history* / Q000706:statistics & numerical data; D014481:United States
D003276:Contraceptives, Oral