title: Twin research: past and present.
mesh_terms: D001724:Birth Weight; D001835:Body Weight; D005260:Female; D005826:Genetics, Medical; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic