Turns out abstinence pledges are dangerous:
By 2001, Dr Rosenbaum found, 82 per cent of those who had taken a pledge had retracted their promise, and there was no significant difference in the proportion of students in both groups who had engaged in any type of sexual activity, the age at which they first had sex or their number of sexual partners. ¶ But the percentage of students who reported condom use was about 10 points lower for those who had taken the pledge, and they were about 6 percentage points less likely to use any form of contraception.