Twin gestation.
D001724:Birth Weight; D036861:Delivery, Obstetric; D005260:Female; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D008297:Male; D008428:Maternal Mortality; D009519:New York City; D011247:Pregnancy; D011248:Pregnancy Complications; D014427:Twins