That study doesn't say anything about what the chance of a raped woman getting pregnant is. In fact the sample is 16 women from a village in Guatemala. How does their miscarriage rate prove anything about the chance of conception among women who were raped?
Isn't it a leap of faith to assume rape produces cortisol and stress at a high enough rate to stop conception? Wouldn't it be better to look at the pregnancy rate for rape victims and the chance of getting pregnant from one-time unprotected sex? This report indicates pregnancy rate of 5% from rape and a 3.1% of getting pregnant from one-time unprotected sex.