Monitoring High-Risk Canine Pregnancies for Fetal Distress

A pregnant bitch may appear clinically normal even when changes affecting fetal development or viability are already underway. For the practicing veterinarian, periodic pregnancy assessment provides an opportunity to identify abnormalities earlier and to follow fetal and maternal status as pregnancy progresses. Ultrasonography, Doppler evaluation and fetal heart-rate assessment can provide complementary information when a pregnancy requires closer monitoring. 

Use Ultrasonography to Follow Pregnancy Development 

Periodic examinations are recommended to evaluate pregnancy progression. When performed by an experienced operator, ultrasonography can help detect abnormalities before they become clinically obvious. 

Changes that may raise concern include: 

• Reduced diameter or abnormal contour of the gestational vesicle

• Lack of fetal viability

• Increased placental thickness

• Increased fluid echogenicity

• Increased resistivity index (RI) and pulsatility index (PI) of the uteroplacental arteries¹ 

These changes have been associated with the onset of embryo resorption around the second and fourth weeks of gestation¹.

Ultrasonographic abnormalities may become apparent long before visible clinical signs, making serial assessment particularly useful when pregnancy pathology is suspected.

Assess Fetal-Maternal Blood Flow 

Doppler ultrasonography can provide additional information about fetal-maternal circulation. The umbilical artery and fetal renal artery can be evaluated, with abnormal parameters suggesting gestational pathology¹.

Uterine and umbilical arterial blood-flow patterns can differ between small, medium and large breeds during the second half of pregnancy. In contrast, fetal heart rate does not vary between these breed groups during the same period². Breed-related physiological variation should therefore be considered when interpreting Doppler findings rather than treating every difference as evidence of pathology.

Monitor Fetal Heart Rate Carefully 

Fetal heart rate provides an important indicator of fetal status. A normal maternal heart rate is approximately 70–120 beats per minute, while fetal heart rate is generally between 180 and 220 beats per minute¹. Fetal distress is most commonly associated with fetal bradycardia and changes in fetal heart rate.

However, a single fetal heart-rate value does not always provide the complete picture. The fetal-to-maternal heart-rate ratio can provide a more informative assessment because it reflects fetal status in relation to maternal status¹. Combining this assessment with Doppler examination allows comparison of uteroplacental and umbilical arterial blood flow in normal and abnormal conceptuses.

Consider Ductus Venosus Assessment 

Doppler evaluation of the ductus venosus (DV) waveform may also provide prognostic information. Litters in which three-phase DV waves were detected had an almost 21-fold higher chance of neonatal mortality, defined as one or more dead puppies per litter, compared with litters showing two-phase waves³.

Non-invasive color flow mapping can also be used after birth to confirm or exclude closure of the DV during the first 10 days of life. This may have value when early assessment is required in puppies from breeds predisposed to congenital portosystemic shunts⁴.

Key Takeaways 

• Use periodic pregnancy examinations to follow fetal development and identify abnormalities.

• Ultrasonography can detect changes in gestational structures, placental appearance and fetal viability before obvious clinical signs develop.

• Assess uteroplacental, umbilical and fetal renal arterial blood flow when Doppler evaluation is indicated.

• Consider breed-related physiological differences when interpreting Doppler findings.

• Monitor fetal heart rate, with 180–220 bpm described as the normal fetal range.

• The FHR/MHR ratio can provide additional information beyond fetal heart rate alone.

• Doppler assessment of the ductus venosus may provide additional prognostic information regarding neonatal survival.

A structured approach combining serial ultrasonography, Doppler findings and fetal heart-rate assessment can give the veterinarian a clearer picture of pregnancy progression and fetal well-being. The aim is to recognize concerning changes early enough to allow appropriate reassessment and management of the bitch and her developing litter. 

References 

1. Uchańska O, Ochota M, Eberhardt M, Niżański W. Dead or alive? A review of perinatal factors that determine canine neonatal viability. Animals. 2022 May 30;12(11):1402. https://www.mdpi.com/2076-2615/12/11/1402 

2. Blanco PG, Huk M, Lapuente C, Tórtora M, Rodríguez R, Arias DO, Gobello C. Uterine and umbilical resistance index and fetal heart rate in pregnant bitches of different body weight. Animal reproduction science. 2020 Jan 1;212:106255. https://www.academia.edu/download/101309159/j.anireprosci.2019.10625520230420-1-jzpfpw.pdf 

3. Barella G, Faverzani S, Faustini M, Groppetti D, Pecile A. Neonatal mortality in dogs: Prognostic value of Doppler ductus venosus waveform evaluation-Preliminary results. Veterinary World. 2016 Apr 7;9(4):356. https://pmc.ncbi.nlm.nih.gov/articles/PMC4864475/pdf/VetWorld-9-356.pdf 

4. Van den Bossche L, Van Steenbeek FG. Canine congenital portosystemic shunts: Disconnections dissected. The veterinary journal. 2016 May 1;211:14-20. https://research-portal.uu.nl/ws/files/28436057/Canine.pdf