Contributors: Autumn P Davidson

 Species: Canine   |   Classification: Miscellaneous

Rationale

  • Pregnancy diagnosis and subsequent examinations are important because:
    • Owners can sell puppies while they are still in utero.
    • The fertility of a stud dog can be proven.
    • Normal gestation and fetal health can be confirmed.
    • Stud fees can be paid on the basis of a positive pregnancy diagnosis.
    • Owner can prepare for the parturition.
    • Single puppy syndrome can be confirmed and managed appropriately.
    • Non-gravid females need not be treated unnecessarily to terminate pregnancy.
    • Differentiate failure to conceive vs. resorption.
    • Permits therapy as indicated or uterine irritability/pre-term labor in conjunction with tocodynamometry.
    • Permit early evaluation for failure to conceive.

Technique

  • In all cases, days of gestation are counted from the LH surge (64-66 days) or the initial rise in progesterone suggesting the LH surge; or 56-58 days from the first day of diestrus.
  • Gestation from breeding dates can normally range from 58-72 days.
  • When in doubt, repeat the pregnancy evaluation using multiple methods to age the gestation (see below).

Transabdominal palpatation

  • Useful technique but lacks sensitivity and specificity.

Procedure

  • Position animal in standing restraint.
  • Best time to palpatate the feto-placental units is between 25 and 30 days gestation. Before this, they are not clearly palpable and afterwards the placental units lose their individual spherical shape.
  • Abdominal distension may be present from about 5 weeks.
  • During last week of gestation, fetal heads can be palpated or seen moving.
  • Results depend more on the state of relaxation of the bitch than the years of experience of the operator.

Ultrasonography

  • Uterine ultrasonography Ultrasonography: uterus is the method of choice.
  • First reliable at 25 days gestation, straightforward at 30 days gestation.

Equipment

  • Small animal patients are best evaluated using an ultrasound machine equipped with a curvilinear variable frequency scanhead (6.0-8.0 MHz).

Procedure

  • Position animal in dorsal recumbency. Standing is useful in giant breeds or uncooperative bitches, but is not as easy.
    The use of a padded V-trough is helpful.
  • Clipping is not advised due to the presence of delicate mammary development and not usually necessary as ventral alopecia occurs with pregnancy.
  • The use of acoustic coupling gel improves the image.
  • Optimally, a full bladder prior to the examination serves as a useful landmark and may facilitate examination of structures distal to the bladder.
  • The normal 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 Uterus: normal - ultrasound.
  • The full urinary bladder acts as an acoustic window to improve imaging the uterus. The cervix is located slightly cranial to the bladder trigone and is best seen when under hormonal influence rather than during anestrus.
  • Start the pregnancy scan by transversely locating the urinary bladder, colon and uterine body as described earlier. Once the uterine body has been identifed, sweep cranially still in transverse, along each horn towards each kidney. Follow each uterine horn to its ovary.

Results

  • At 30-32 days gestation the vesicle is larger than transverse small bowel, making identification easy Uterus: early pregnancy (25 days gestation) - ultrasound.
  • Each fetus is contained in an oval, fluid filled gestational sac Uterus: pregnancy (gestational sac) - ultrasound.
  • Determine fetal viability. The flicker of the heartbeat is regularly seen even without Doppler after 25-28 days gestation. Normal canine fetal heartrates should be >180-200. Uterus: pregnancy (fetal cardiac motion) - Doppler ultrasound.
  • Litter size determination is best at //www.vetlexicon.com30 days gestation. The vesicles are small enough to allow easy counting of fetuses within each uterine horn. In later gestation (>45-50 days) the fetuses are so large the uterine horns overlap making the correct count difficult.
  • The determination of gestational age can be of vital importance. An accurate determination of gestational length can be difficult, especially if numerous copulations occurred and no ovulation timing was performed. Prolonged gestation is a form of dystocia.
  • Normal gestation in the bitch is 56-58 days from the first day of diestrus (detected by serial vaginal cytologies, defined as the first day that cytology returns to <50% cornified/superficial cells), 64-66 days from the LH surge or the initial rise in progesterone from baseline (generally >1.5 ng/mL), or 58-72 days from the first instance that the bitch permitted breeding.
  • Predicting gestational length without prior ovulation timing is difficult because of the disparity between estrual behavior and the actual time of conception in the bitch, and the length of time semen can remain viable in the bitch reproductive tract (often up to >7 days). Breeding dates and conception dates do not correlate closely enough to permit very accurate prediction of whelping dates. Additionally, clinical signs of term pregnancy are not specific: radiographic appearance of fetal skeletal mineralization varies at term, fetal size varies with breed and litter size, and the characteristic drop in body temperature (typically less than 99°F/37°C) may not be detected in all bitches and varies in many. Breed, parity and litter size can also influence gestational length.
  • Gestational aging can be performed using the gestational sac diameter, crown rump length or biparietal/head diameter most easily Uterus: pregnancy (gestational sac measurement) - ultrasound Uterus: pregnancy (fetal age measurement) - ultrasound Uterus: late pregnancy - ultrasound.

Formulas to predict gestational age and days before parturition in the dog

  • Gestational age (GA) is based on days post luteinizing hormone (LH) surge in the dog. Gestational sac diameter (GSD), crown-rump length (CRL), head diameter (HD), and body diameter (BD) measurements are in centimeters. Days before parturition (DBP) is based on 65 +/- 1 days post LH surge in the dog.
  • Gestational age in the dog (+/- 3 days):
    • Less than 40 days:
      • GA = (6 x GSD) + 20
      • GA = (3 x CRL) + 27
    • Greater than 40 days:
      • GA = (15 x HD) + 20
      • GA = (7 x BD) + 29
      • GA = (6 x HD) + (3 x BD) + 30
  • Days before parturition in the dog:
    • DBP = 65 - GA.

Radiology

  • Valuable for determining/confirming the number of fetuses near term.
  • Insensitive for early diagnosis of fetal death as dependent on post-mortem changes.
  • Permits evaluation of bitch's pelvic anatomy.
  • See abdominal radiography Radiography: abdomen.

Results

  • In last 1.5-2 weeks of gestation, the whole fetal skeleton can be seen and skulls can be counted to determine the number of puppies. The danger of malformation due to ionizing radiation is absent at this stage of gestation. A single lateral view is optimal, a second, VD view should be taken only if necessary.
  • If a puppy has died, it will usually show extreme kyphosis, 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 well-being Uterus: fetal death - Doppler ultrasound.
  • Within 2-3 days of parturition, the teeth become radiopaque (facilitated by digital radiography) and can serve as an indication that a Caesarean delivery can be safely performed when ovulation timing is lacking Uterus: fetal dentition - radiograph.
  • Radiography after 55-60 days gestation is most valuable for the evaluation of fetal size. Note that skull size (seen radiographically) does not equate to shoulder or rump size (which is usually contributory to obstructive dystocia Dystocia ; be conservative in evaluation of fetal-maternal size mismatch Uterus: dystocia 02 - radiograph lateral.

Diagnostic testing

  • Relaxin assy is specific for placental tissue, used 25 days post gestation.
  • False negatives can occur with small litter size; does not evaluate fetal viability or give litter size.