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| Jean K. Reichle, DVM, MS, Diplomate,
American College of Veterinary Radiology Ohio State University College of Veterinary Medicine Columbus, Ohio The diagnosis of pregnancy is generally achieved by 3 means in the cat: abdominal palpation, ultrasonography, and radiography. Unfortunately, physiological testing of hormone levels (which is commercially available in dogs) is not available for cats. Changes in behavior, weight gain, and nipple enlargement may signify pregnancy or pseudopregnancy, and are therefore not entirely reliable. Abdominal palpation, when performed by an experienced veterinarian, may reveal 1-2 cm round swellings, most easily detected in early to mid-pregnancy (days 15-30). This is a manual skill best performed by an experienced veterinarian. It is often difficult to palpate a tense, nervous cat and occasionally normal structures, such as fecal material in the colon, can be difficult to differentiate from a fetus. Ultrasonography is best performed while the cat is on its back or side, and the hair on the belly clipped to allow contact between the ultrasound transducer and skin. Gel or rubbing alcohol is used as a ńcoupling agent,î since any small pockets of hair trapped in fur will prevent the ultrasound waves from penetrating in to the patientÍs abdomen. The uterus is identified between the urinary bladder and colon when small. As it distends, it can be more easily identified as tubular loops on the left and right side of the abdomen, between the kidneys and bladder. Ultrasonography is best for identification of pyometra or pregnancy, estimation of gestational age, and evaluation of fetal vitality. A skilled, experienced veterinary ultrasonographer can detect uterine enlargement by day 4 of gestation, however this may be difficult to differentiate from a fluid filled uterus seen with pyometra. The gestational sacs (blastocyst) may be identified as early as 11 days. Fetal cardiac activity may be recognized at day 16. A recognizable fetal head and body can be identified as early as day 26. This is important since biparietal diameter (the width of the fetal head) has been documented as a means of predicting gestational age of the fetus, therefore allowing the determination of a due date. This has been studied in cats by measuring the biparietal diameter in the dorsal plane and body diameter at the level of the liver and stomach. These images must be symmetrical for accuracy. Generally, the image is frozen on the ultrasound monitor screen and internal calipers are used to measure the distances. Multiple measurements in centimeters (cm) should be averaged. These were established in domestic shorthairs, therefore it may vary for breeds with great variations in conformation, such as Persians and Siamese. Equations are available to determine days till delivery (not gestational age, which is from the date of conception): Days prepartum = 43.5 - [10.9 x (Biparietal diameter in cm)] = 61.2 - [24.6 x (Body Diameter in cm)] Estimation of litter size with ultrasound becomes less accurate as the number of kittens increase, and as the pregnancy is in its late stages, since ultrasound cannot evaluate the entire uterus in one instance. The ultrasound probe, at the site of skin contact, can only visualize a small field therefore kittens can be counted more than once or multiple times. Ultrasound is frequently performed to assess viability of the kittens: the heart rate (approximately 120-140 beats per minute) and motion of a fetus is important. Heart rate and fetal movements decrease when a fetus is stressed. The fetus must be mineralized (as early as day 37 of gestation in cats) in order for it to be recognized on a radiographic image. This mineralization progresses over time, therefore the best image of the kittens will be later in pregnancy, close to parturition. An early x-ray image may simply reveal an enlarged uterus, which is not easily differentiated from pyometra. The benefits of radiography over ultrasound are that the number of kittens can be determined (most accurately when taken in late pregnancy, to allow fetal mineralization), and assessment of the size of the fetus versus the motherÍs pelvic canal. Kittens are counted on the radiograph by numbering the heads. This is usually easiest on the lateral view (taken with the cat lying on one side). The pelvic diameter is best evaluated on a straight ventrodorsal view (with the cat on her back), and then compared to fetal head and shoulder width. Fetal vitality and position relative to the pelvic canal can also be assessed. Gas surrounding the fetus but not within the motherÍs intestinal tract, or collapse of the skull bones, are signs of fetal death. The method of pregnancy determination will depend upon the needs of each individual and the availability of equipment and the experience of the people involved. Ask your veterinarian who performs the ultrasound examination; ideally, a board-certified radiologist or ultrasound technologist will have the most experience and can give the most information. References A Davidson, TG Nyland, T Tsutsui. Pregnancy diagnosis with ultrasound in the domestic cat. Veterinary Radiology 1986;27:109-114. K Beck, CJ Baldwin, WTK Bosu. Ultrasound prediction of parturition in queens. Veterinary Radiology 1990;31:32-35. K Miles. Imaging pregnant dogs and cats. The Compendium: Small Animal. 1995;17:1217-1226. # 1 ultrasound view of the fetal chest # 2 radiographs with the heads of 4 kittens numbered # 3 radiographs with the heads of 4 kittens numbered # 4 ultrasound of fetal head Copyright ©2000-2004 SGENews Photo Gallery |
| Pregnancy Diagnosis in the Cat |
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