6Patel RR, Peters TJ, Murphy DJ,et al. Prenatal risk factors for cae- sarean section. Analyses of the ALSPAC cohort of 1,2, 944 women in England [ J ]. Int J Epidemiol,2005,34 ( 2 ) :353 - 367.
7Eriksen LM,Nohr EA,Kjaergaard H. Mode of delivery after epid-u- ral analgesia in a cohort of low-risk nulliparas[ J]. Birth, 201,1. ,38 (4) :317 -326.