For patients of the EA group who were undergoing controlled ovarian hyperstimulation , EA stimulation ( 5 Hz/20 Hz , 15-20 V ) was applied to bilateral Shenshu ( BL 23 ) , Qihai ( CV6 ) , bilateral Zusanli ( ST 36 ) - Sanyinjiao ( SP 6 ) , and bilateral Neiguan ( PC6 ) - Zigong ( EX-CA 1 ) for 30 min , once daily till accepting embryo transplant .