Contributors: David Godfrey, Rob Lofstedt, Autumn P Davidson

 Species: Feline   |   Classification: Miscellaneous

Rationale

  • Pregnancy diagnosis and subsequent examinations are important because:
    • Permits better cattery husbandry when pregnancy is confirmed.
    • Permits earlier evaluation for failure to conceive.
    • Owners can home/sell kittens while they are still in utero.
    • The fertility of the male can be proven.
    • The health of the pregnancy and fetal viability can be monitored. 
    • Gestational aging is possible.
    • Stud fees can be paid on the basis of a positive pregnancy diagnosis.
    • Owner can prepare for the parturition Parturition.
    • Single kitten syndrome can be confirmed and managed appropriately.
    • Non-gravid females need not be treated unnecessarily to terminate pregnancies.

Techniques

Transabdominal palpatation

  • Useful technique but is not specific for healthy pregnancy.
  • Inexpensive and easy to perform in nonfractious queens.

Procedure

  • Position animal in standing restraint.
  • Best time to palpate the feto-placental units is between 20 and 30 days of gestation. Before this, they are not clearly palpable, and afterwards the placental units lose their spherical shape and become softer and less individualized.
  • Abdominal distension may be present from about 5 weeks.
  • After day 45, fetal heads can be palpated.
    Breeders refer to 'pinking up' (hyperemia of the teats) as a confirmation of pregnancy at 3-4 weeks.

Results

  • Decreased or resorbing fetuses Retained fetal membranes / retained fetus cannot be readily differentiated from healthy normal fetuses.
  • Uterine swelling secondary to pyometra Pyometra, mucometra, hydrometra or neoplasia can be mistaken for pregnancy   Abdomen: closed pyometra - ultrasound  .
    Results depend more on the relaxed state of the animal than the years of experience of the operator.

Ultrasonography

  • Method of choice.
  • Equipment:
    • Small animal patients are best evaluated using an ultrasound machine equipped with a curvilinear variable frequency scanhead (6.0-8.0 MHz) Ultrasonography: uterus.
  • Procedure:
    • Position animal in dorsal recumbency.
    • Clipping is not advised due to the developing mammary glands and normal ventral alopecia associated with pregnancy.
    • Acoustic coupling gel is advised to improve the image obtained.
  • Results:
    • The uterus is best located by scanning transversely between the urinary bladder and the colon. The cervix and uterine body are seen as a continuous hypoechoic round structure dorsal to the anechoic urinary bladder and ventral to the hyperechoic, crescent shaped colon. The full urinary bladder acts as an acoustic window to improve imaging the uterus.
    • Start the pregnancy check scan by transversely locating the urinary bladder, colon and uterine body as described earlier. Once the uterine body has been identified, sweep cranially, still in transverse, towards each kidney. Follow each uterine horn to its ovary. Each fetus is contained in an oval, fluid filled gestational sac.
    • Definite ultrasonographic diagnosis of pregnancy in the queen based on the appearance of a "fetal pole" can be made at 15-17 days post coitus, although gravid uterine enlargement (4-14 days) and the presence of a gestational sac (11-14 days) can be detected even earlier   Abdomen: early pregnancy - ultrasound  . 
    • Ultrasonography permits evaluation of early fetal cardiac motion (21-22 days post LH peak), fetal movement (31-32 days post LH peak) and the fetal heart rate, enabling assessment of viability. The normal fetal heart rate in the cat is >200 beats per minute and heart rates are detectable as early as 25 days post mating   Abdomen: pregnancy 30 days gestation 01 - ultrasound  .
    • By 30 days gestation (30 days after the LH surge) pregnancy diagnosis with ultrasonography is straightforward   Abdomen: pregnancy 30 days gestation 02 - ultrasound  .
    • Between 20-30 days gestation, the vesicles are small enough to allow easy counting of fetuses within each uterine horn. In later gestation (>50 days) the fetuses are so large the uterine horns overlap making the correct count difficult.   Abdomen: normal pregnancy - ultrasound 02    Abdomen: normal pregnancy - ultrasound 01 
    • Fetal age determination by ultrasonography is accomplished in two ways:
      • 1. The first appearance of visible structures and
      • 2. The measurement of certain parameters.  Predicting fetal age by noting the first appearance of visible structures corresponding to gestational length is often more accurate than measurements. Measurements such as the gestational sac diameter, fetal occipitosacral (crown-rump length) and fetal skull (biparietal) diameter can be obtained ultrasonographically, relate closely to fetal age, and permit estimation of gestational length and parturition dates, especially useful if ovulation timing was not performed. Variation in breed size and individual variation in measuring technique are sources of inaccuracy in predicting fetal age with ultrasound.    Abdomen: fetal age measurement 01 - ultrasound      Abdomen: fetal age measurement 02 - ultrasound 

Formulas for feline gestational aging 

  • Gestational aging using biparietal diameter (HD) or body diameter (BD):
    • Gestational age (GA) in the cat (+/- 2 days)
    • Greater than 40 days gestation:
      • GA = 25 x HD +3
      • GA = 11 x BD +21
    • Days before parturition in the cat:
      •  DBP = 61- GA.
  • Feline gestational aging using crown rump length:
    • Y = 0.2423 x GA - 4.2165
    • Y is mean litter Crown Rump Length (cm)
    • GA is the gestational age  (Solve for GA).
  • Ultrasonography is less accurate than radiography in estimating litter size, particularly later in gestation, due to its dynamic nature. Keep in mind that fetal resorption or abortion Pregnancy loss (resorption and abortion) can alter litter size after early ultrasound estimates are made.
  • Ultrasonography permits accurate evaluation of fetal death. Lack of cardiac motion is evident followed by morphologic changes leading to resorption or abortion   Abdomen: fetal death - ultrasound  .

Radiology

  • See abdominal radiography Radiography: abdomen 
  • Valuable for determining the number of fetuses, fetal viability and fetal development   Uterus: normal pregnancy (near term) - radiography  .

Results

  • Uterine enlargement can be seen from about 17 days but this technique does not distinguish pregnancy from pathological enlargement until fetal skeletons can be seen.
  • Radiography cannot be used to assess fetal viability in a timely fashion. Once profound post mortem changes have occurred, radiography can detect intra-fetal gas accumulation or abnormal skeletal arrangement suggesting fetal death. Early fetal resorption cannot be detected radiographically, only by ultrasound.
  • In the last 2 weeks of gestation, the whole fetal skeleton can be seen and skulls can be counted to determine the number of kittens.
  • If a kitten has died, it will usually show extreme kyphosus, bending into a tight 'C' posture. Gas may be detected in the fetus and sometimes the bones of the calvarium will be seen to overlap. However, these changes are frequently not present, especially if a fetus has died recently. Therefore, ultrasound is far more sensitive for examining fetal wellbeing.
  • Within 2-3 days of parturition, the teeth become radiopaque and can serve as an indication that a Caesarean delivery Cesarean section can be safely performed.