Multiple births in Poland in 1949-1971.
D001723:Birth Rate; D005260:Female; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D010298:Parity; D011044:Poland; D011247:Pregnancy; D013223:Statistics as Topic; D014310:Triplets; D014427:Twins