Recent secular trends in multiple birth rates.
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D000328:Adult; D001723:Birth Rate / Q000639:trends*; D004739:England; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008423:Maternal Age; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000706:statistics & numerical data*; D014852:Wales