How Badly Do We Need to Know? Part 2
Are routine prenatal x-rays in dogs safe? Over the last 30 years, there has been a dramatic decrease in routine x-rays of pregnant women due to concerns for the safety of their unborn babies.
In my last blog, I challenged the prevailing notion that routine prenatal x-rays in dogs have been shown to be safe and in fact, presented studies showing that fetal irradiation may increase early and lifetime cancer in dogs.
Since the publication of that blog, the discussion has been quite passionate with many breeders claiming that x-rays have never harmed their puppies. Because radiation damage often takes years to reveal itself, it is easy to overlook any possible connection. Heck, I’ll bet many breeders can’t remember if they x-rayed a litter that is now five or even seven years old. In addition, determining if there is a relationship between x-rays and cancer requires large numbers of pups, as well as cause and date of death on all of them. Few breeders have either the numbers or the data to draw a conclusion either way.
But isn’t avoiding ONE dog with early cancer worth it?
It sure seems to be in the human medical and dental world given the restrictions of x-raying pregnant women. To quote the FDA guidelines to physicians and pregnant women, “…the risk of not having a needed x-ray could be much greater than the risk from the radiation. But even small risks should not be taken if they’re unnecessary.” (emphasis mine)
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During most x-ray examinations – like those of the arms, legs, head, teeth, or chest – your reproductive organs are not exposed to the direct x-ray beam. So these kinds of procedures, when properly done, do not involve any risk to the unborn child. However, x-rays of the mother’s lower torso – abdomen, stomach, pelvis, lower back, or kidneys – may expose the unborn child to the direct x-ray beam. They are of more concern. (Again, emphasis mine.)
Even indirect, low-dose radiation, such as that from dental films, can effect fetuses as found in a 2004 study that showed dental x-rays resulted in low birth weights of full-term babies. In dogs like humans, low-birth weight carries short- and long-term risks to babies.
Furthermore, the absorbed dose of radiation varies by the quality of the x-ray machine, competence of the operator and the size of the patient. Smaller patients absorb more radiation so we would expect direct radiation of a small fetus to result in higher absorption rates than the same x-ray of an adult.
We stopped doing routine, prenatal x-rays in 2004 and although our data are not perfect by any means, here are our findings.
Since we quit routinely x-ray our pregnant bitches, our early cancer (before 9 years of age) rates dropped from 13% to less than 8%! Furthermore, the age at which early cancers appeared increased by more than 2 years, from 5.5 to 7.9 years of age. If we look at deaths prior to 11 years of age, we lost 23% of our x-rayed dogs to cancer but only 12% of those that were not x-rayed. Still not as good as we want it to be, but a whole lot better than it was in 2003!
Since we quit routinely x-ray our pregnant bitches, our cancer rate before 11 years dropped by from 23% to 12%!
Now mind you, this is a small dataset from a single golden retriever breeding program. It is by no means definitive support for stopping x-rays for several reasons. First, since this is only our breeding program, the numbers are pretty small. Despite that, the difference in cancer rates is statistically significant. However, a larger study would provide clearer results.
Second, although we have bred the same lines over this 25-year period, we included many outside sires in our breeding program so perhaps they influenced our dogs’ longevity. And finally, since this was not a formal study, we did not hold constant other aspects of our dogs’ care. So let’s just add it to the study we mentioned in our last blog as our first clues that perhaps routine, prenatal x-rays aren’t as safe as assumed.
You may be in a breed that has very low cancer rates, so fetal x-rays in dogs might not be of concern to you. But for those of us who have breeds with very high cancer rates, like goldens, Berners, boxers, flat-coats and more, need to scrutinize every step we take in producing and rearing our puppies so the choices we make don’t contribute to the problem.
Why Do Dog Breeders X-Ray Their Pregnant Dogs?
Given the potential danger, why do breeders routinely x-ray pregnant bitches? Most do it to get a puppy count prior to whelping. I understand how comforting it is to know exactly how many puppies to expect.
Yet if x-rays are so accurate for puppy counts, why is Facebook filled with posts of x-rays asking breeders and vets to GUESS at the number of pups? And why do the numbers vary, even among experienced breeders? Even vets in the same practice play the Guessing Game, often differing in counts by up to 3 pups. Our experience has been similar. We once saw 9 pups on x-ray only to have 12 born. Later, we x-rayed 13, and yet a whopping 15 pups arrived.
I’m also struck by how many x-rays are poorly positioned or developed making guesses nearly impossible or repeat x-rays necessary, now doubling or even tripling the radiation the pups received.
Some of you are probably angry about this blog while others might be intrigued. Even if you are now wondering about the safety of x-rays, you might be wondering, “Oh my gosh, if I don’t x-ray, how will I know how many puppies to expect?” Read our next blog to find out how to count pups more safely.
Read Part 3 of my blog for alternatives to x-raying.
Hujoel, PP, AM Bollen et al. 2004. Antepartum Dental Radiography and Infant Low Birth Weight. Journal of the American Medical Association. 2004 vol 291, iss 16, pp1987-1993.
Linet, MS, TL Slovos, et al. 2012. Cancer risks associated with external radiation from diagnostic imaging procedures. CA: A Cancer Journal for Clinicians, vol 62, iss 2, pages 75–100.
Nickoloff, EL, Lu ZF. 2015. Patient Radiation Doses in Diagnostic Radiology. American Association of Physicists in Medicine Meeting Proceedings.
U.S. Food and Drug Administration. 2014. X-Rays, Pregnancy and You. Accessed at the FDA website.
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