Contraceptive Efficacy Rates for Cervical Barriers and Other Barrier Methods
% of women experiencing an unintended pregnancy within the first year or first 6 months of use

Method Perfect Use Typical Use Typical Use (6 months)
   
Cervical barriers (used with spermicide)
diaphragm 6% 16%  
cervical cap  
  nulliparous women 9% 16%  
  parous women 26% 32%  
Lea's shield 15% 8.7%
FemCap 22% 13.5%
   
Other barrier methods  
male condom 2% 15%  
female condom 5% 21%  
sponge  
  nulliparous women 9% 16%  
  parous women 20% 32%  
spermicide 18% 29% 10-16%

References:

Trussell J. Contraceptive efficacy. In Hatcher et al., Contraceptive Technology: Eighteenth Revised Edition.  New York: Ardent Media, 2004.
Mauck et al., Lea's Shield: a study of the safety and efficacy of a new vaginal barrier method used with and without spermicide. Contraception.    53(6): 329-35; Jun 1996.
Mauck et al., A comparative study of the safety and efficacy of FemCap, a new vaginal barrier contraceptive, and the Ortho All-Flext diaphragm.    Contraception 60(2): 71-80; Aug 1999.
Raymond et al., Contraceptive Effectiveness and Safety of Five N9 Spermicides. Contraception. 103(3): 430-9; Mar 2004.