Just as abortion stats are difficult to quantify because various states require various reporting, reliable stats on pregnancies that result from rape are difficult to find. However, according to the LA Times:
"Because pregnancy is believed to occur with about the same frequency whether a woman was raped or engaged in consensual sex – about 5% of the time – the wildly different estimates in occurrences of rape have produced wildly varying estimates of the number of pregnancies that result."
Statistics on rape and pregnancy are complicated - Los Angeles Times
From the Wall Street Journal:
"The biggest discrepancy is in the estimates used for the number of rapes in the U.S. These can vary in official government estimates from as few as 64,000 a year to as many as 1.3 million, about 20 times larger, depending on when and how rapes are counted.
...The Federal Bureau of Investigation counted 84,767 forcible rapes—as distinct from statutory rapes without force—in 2010, based on crime reports from local law-enforcement agencies. The Department of Justice's National Crime Victimization Survey, based on polling Americans, counted 188,380 rapes and sexual assaults that year. The Centers for Disease Control and Prevention, conducting its own victimization survey, counted 1.3 million rapes in 2010.
Survey design and question wording also matter. A study published in 2000 by the Department of Justice compared two surveys conducted in 1997 among women attending college. The surveys were identical, except that one was modeled on Justice's crime victimization survey while the other asked much more detailed questions to screen for rape. The latter survey estimated a percentage of women who had been raped that was 11 times higher than the one modeled on Justice's survey."
In addition to conflict between the CDC's and Justice's reporting, "The other unknown number is the probability that a rape will lead to pregnancy. There are no fully reliable, up-to-date data on such relevant factors as the age of victims, the rate of their hormonal contraceptive use and what percentage of rapists ejaculate in their victims, researchers say."
Pregnancies From Rape Prove Tough to Count - WSJ.com
Important to note that the Kilpatrick referenced is the author of the 1996 study frequently cited:
Rape-related pregnancy: estimates and de... [Am J Obstet Gynecol. 1996] - PubMed - NCBI