Twinning rates, fertility, and industrialization: a secular study.
D005260:Female; D005298:Fertility; D005313:Fetal Death; D005787:Gene Frequency; D006801:Humans; D007221:Industry; D007231:Infant, Newborn; D007558:Italy; D008423:Maternal Age; D011247:Pregnancy; D014310:Triplets; D014427:Twins