1. Martin JA, Hamilton BE, Osterman MJK: Three Decades of Twin Births in the United States, 1980–2009. 2012, Hyattsville, MD: National Center for Health Statistics, NCHS Data Brief, No. 80, January 2012
2. Martin JA, Hamilton BE, Ventura SJ, Osterman MJ, Kirmeyer S, Mathews TJ, Wilson EC: Births: Final Data for 2009. National Vital Statistic Reports. 2011, Hyattsville, MD, USA: National Center for Health Statistics, no 1, vol. 60
3. Corsello G, Piro E: The world of twins: an update. J Matern Fetal Neonatal Med. 2010, 23 (Suppl 3): 59-62.
4. Giuffrè M, Piro E, Corsello G: Prematurity and twinning. J Matern Fetal Neonatal Med. 2012, 3: 6-10.
5. Corsello G: I Gemelli. Un Profilo Di Medicina Perinatale E Pediatrica. 2010, Cagliari, Italy: Hygeia Press, First