ss74, As I had mentioned earlier, I do agree with you that a single method may not work 100% but I do strongly believe that if you go for combination of methods, you can guarantee 99.99%. Natural family planning method alone (without any contraceptive, birth control pills) can be 90% to 98% effective (2 to 10 pregnancies per 100 couples) when they are practiced correctly. Source: http://familydoctor.org/126.xml. And, how do you define the vague word "unexpected pregrancy" ?