From the Centers for Disease Control and Prevention. State-specific variation in rates of twin births--United States, 1992-1994.
D001723:Birth Rate; D003237:Connecticut / Q000453:epidemiology; D006801:Humans; D008404:Massachusetts / Q000453:epidemiology; D008423:Maternal Age; D014427:Twins / Q000706:statistics & numerical data*; D014481:United States / Q000453:epidemiology