Diagnostic imaging in Linnaeus's two-toed sloth (Choloepus didactylus) – pregnancy diagnosis and fetometry

Purpose: The knowledge of the reproductive physiology and biology of the two-toed sloth is fragmentary at best. So the data of the gestation period in the literature vary from 150 to 322 days. This study is intended to demonstrate the pregnancy diagnosis and the fetometry in the two-toed sloth with ultrasonography.

Material and methods: The ultrasound investigations to visualize the genital system in this species can be performed transcutaneous or transrectal. Only the transcutaneous examinations can be performed without immobilization, if the animals are in medical training. The transcutaneous pregnancy examination is executed with a transducer frequency from 6 to 10 MHz. In total 23 pregnancies (n = 10 animals) were sure diagnosed. The ultrasound investigations were also used to detect the fetal development (n = 8 animals).

Results: The first indication of an existing pregnancy is the visualization of the gestational sac at the end of the first month of pregnancy. With the beginning of the second month of the gestation period, the embryo is detectable. In the same gestation month the cardiac activity can also be recognized. The crown-rump length of the fetus is only measurable in the third month. For the following months the fetal development is represented on the biparietal diameter (BPD) and the abdominal diameter (AD).

Conclusion: The total gestation period in a two-toed sloth lasts 330 to 350 days. In a range from 294 to 316 days, the fetal development could be visualized with ultrasound (n = 7 animals). A shorter fetal development of 265 days was registered in one female.