1. Births: final data for 2001;Martin;Natl. Vital Stat. Rep.,2002
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3. Intrapartum management of twin gestation;Adams;Clin. Obstet. Gynecol.,1990
4. Management of twin pregnancy: the vaginal route is still safe;Laros;Am. J. Obstet. Gynecol.,1988
5. Intrapartum external version of the second twin;Chervenak;Obstet. Gynecol.,1983