1. Statistics Canada. Table 102–4513—Live births, weeks of gestation indicators, by characteristics of the mother and child, Canada, annual, CANSIM (database). Available at: http://www5.statcan.gc.ca/cansim/a47. Accessed February 28, 2013.
2. Trends in twin birth outcomes and prenatal care utilization in the United States, 1981–1997;Kogan;JAMA,2000
3. Determinants of preterm birth rates in Canada from 1981 through 1983 and from 1992 through 1994;Joseph;N Engl J Med,1998
4. Management of twin pregnancies (Part 1), SOGC Consensus Statement, no. 91, July 2000;Barrett;J Soc Obstet Gynaecol Can,2000
5. Births: Final data for 2007;Martin;Natl Vital Stat Rep,2010