1. 1 SJ Ventura, JA Martin, SC Curtin, and TJ. Matthews Births: Final Data for 1997. National Vital Statistics Reports; Vol. 47 no. 18. Hyattsville, MD: National Center for Health Statistics, 1998.
2. 2 SM. Taffel Health and Demographic Characteristics of Twin Births: United States, 1988. Vital and Health Statistics; Vol. 21 no. 50. Hyattsville, MD: National Center for Health Statistics, 1992.
3. 3 JA Martin, and MM. Park Trends in Twin and Triplet Births: 1980-97. National Vital Statistics Reports; Vol. 47 no. 24. Hyattsville, MD: National Center for Health Statistics, 1999.
4. Perinatal mortality in twins and singletons matched for gestational age at delivery at ≥30 weeks