I am a big big fan of ultrasounds. The development of this imaging technique in veterinary medicine was, for sure, a huge breakthrough. By allowing us veterinarians to better visualize what is going on « inside » our patients, it gives us a better understanding of many clinical situations. Briefly: simply an amazing diagnostic tool. The same goes for its use in small animal reproduction. I often said to our vet students that I could not imagine practicing this discipline without an ultrasound machine. One thing this technique is of particular interest for: visualizing embryonic resorptions.
Indeed, I am often asked which tests I would recommend to perform on bitches/queens that suffered from infertility. A pregnancy diagnosis by ultrasounds is always on my list. Why? Because I want to know if there are, or not, embryonic resorptions.
What is an embryonic resorption?
Look at the two picture below. On the left, you can see a normal viable embryo (during the live exam, you would even be able to visualize its heartbeats!). On the right, an embryonic resorption: an embryo whose development started but, somehow along the way, stopped.
Ultrasounds are often the only way to properly detect them, because any pregnancy arrest that occurs before 35 days of gestation might get totally unnoticed: the embryos will just be « digested » by the uterus, and there will be no other clinical sign at all...
Embryonic resorptions: what are the causes?
Is it always abnormal to detect embryonic resorptions during an ultrasound examination? Definitely not: sometimes when the embryos are not fully viable (because they carry a severe genetic defect for instance), they will die in utero and be reabsorbed. However, depending on the clinical context (for instance an animal with history of infertility) or when several embryonic resorptions are visualized during the ultrasonographic exam, this might raise some clinical concerns from the attending veterinarian. "Something" might not be right... and more complementary tests will be required in order to investigate the situation.
In small animals, three main causes can usually lead to "abnormal" embryonic resorptions:
- Infectious diseases: Whichever species you are dealing with, this is always something to consider when confronted to fertility issues. In dogs we will always need to rule out canine brucellosis (see our previous post). In cats it will be the Feline Leukemia Virus (FeLV). Other pathogens can also be involved (the list goes on and on). The most common ones are listed in the Table below.
Table 1: Main causes of embryonic resorptions in canines and felines
- Hormonal causes: luteal failure - an inability to produce/maintain progesterone secretion, the key hormone to maintain pregnancy - has been described in bitches and queens. When dealing with embryonic resorptions, this is why your veterinarian might recommend to perform a progesterone assay. Other hormonal disbalances (related to estrogens or thyroid hormones) can also have an impact on the embryonic development.
- Uterine diseases: alterations of the uterine tissue (cystic endometrial hyperplasia, endometritis, etc) can prevent proper embryonic implantation inside the uterine wall and lead, as a consequence, to visualization of embryonic resorptions. Any uterine disease that lead to modifications of the uterine medium/architecture can have the same consequences.
What can be done?
That’s why the realization of a pregnancy diagnosis is so important in the infertile bitch/queen. Visualizing embryonic resorptions tells the clinician that 1/ fertilization did occur (keep in mind that absence of fertilization is both in canines and felines the first cause of infertility) 2/ there is “something” interfering with the normal course of the gestation. Identifying the exact nature of this “something” can sometimes be tricky, but thanks to recent advances in the field of small animal reproduction, veterinarians now have access to much more options to clearly find out what is going on (an example here with uterine biopsies).
As soon as we know what causes the issue, we can figure out the best course of action. Each cause we mentioned earlier requires a specific approach. If we know what we have to fight, we automatically become more efficient. However, if you did not perform an ultrasound and you did not see the embryonic resorptions, you understand now why it becomes more difficult to get to this point…
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