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Early Development and Implantation
Early Development and Implantation
• Fertilization Location: Occurs in the oviducts for both species.
• Fertilization Location: Occurs in the oviducts for both species.
• Implantation Timing:
• Implantation Timing:
◦ Dogs: Approximately 18 days after fertilization.
◦ Dogs: Approximately 18 days after fertilization.
◦ Cats: Approximately 14 days after fertilization.
◦ Cats: Approximately 14 days after fertilization.
• Uterine Changes: Small swellings called deciduomata form along the uterine horns by roughly day 21.
• Uterine Changes: Small swellings called deciduomata form along the uterine horns by roughly day 21.
Physical Palpation
Physical Palpation
• Early Pregnancy: Deciduomata are palpable by day 21 (in cooperative animals) and double in diameter every 7 days due to rapid fetal growth.
• Early Pregnancy: Deciduomata are palpable by day 21 (in cooperative animals) and double in diameter every 7 days due to rapid fetal growth.
• Mid-Pregnancy: Between days 35–38, these swellings become less distinct, making palpation more difficult.
• Mid-Pregnancy: Between days 35–38, these swellings become less distinct, making palpation more difficult.
• Late Pregnancy: Fetal heads and rumps become palpable as firm, nodular structures in the ventral caudal abdomen.
• Late Pregnancy: Fetal heads and rumps become palpable as firm, nodular structures in the ventral caudal abdomen.
Diagnostic Testing and Assays
Diagnostic Testing and Assays
• Relaxin Assay: A commercial assay is available for dogs that is specific and sensitive for pregnancy diagnosis after 30 days of gestation.
• Relaxin Assay: A commercial assay is available for dogs that is specific and sensitive for pregnancy diagnosis after 30 days of gestation.
• Differential Diagnosis: Imaging is essential to distinguish pregnancy from other causes of uterine distention, such as:
• Differential Diagnosis: Imaging is essential to distinguish pregnancy from other causes of uterine distention, such as:
◦ Hydrometra.
◦ Hydrometra.
◦ Pyometra.
◦ Pyometra.
◦ Mucometra.
◦ Mucometra.
Ultrasonography and Doppler
Ultrasonography and Doppler
• Optimal Timing: Best performed between 25–35 days of gestation.
• Optimal Timing: Best performed between 25–35 days of gestation.
◦ Note: Testing before 21 days often results in "false-negatives".
◦ Note: Testing before 21 days often results in "false-negatives".
• Fetal Viability: Permits the evaluation of health and allows clinicians to "hear" the fetal heart via Doppler.
• Fetal Viability: Permits the evaluation of health and allows clinicians to "hear" the fetal heart via Doppler.
• Heart Rate: Fetal hearts beat 2–3 times faster than the dam's heart.
• Heart Rate: Fetal hearts beat 2–3 times faster than the dam's heart.
Radiography (X-rays):
Radiography (X-rays):
• Calcification Timing: Skeletal calcification begins as early as day 28 but is not detectable by routine radiography until day 42–45.
• Calcification Timing: Skeletal calcification begins as early as day 28 but is not detectable by routine radiography until day 42–45.
• Safety: Radiography at this stage is not teratogenic (does not cause birth defects).
• Safety: Radiography at this stage is not teratogenic (does not cause birth defects).
• Litter Size: Late gestational radiography (specifically >55 days) is the most accurate method for determining the number of fetuses.
• Litter Size: Late gestational radiography (specifically >55 days) is the most accurate method for determining the number of fetuses.
• Term Confirmation: The appearance of fetal dentition (teeth) indicates the fetus is developed enough for an elective cesarean section.
• Term Confirmation: The appearance of fetal dentition (teeth) indicates the fetus is developed enough for an elective cesarean section.
Calculating Gestational Age:
Calculating Gestational Age:
• Methods: Age can be calculated using various ultrasonographic measurements:
• Methods: Age can be calculated using various ultrasonographic measurements:
◦ Gestational sac diameter (GSD).
◦ Gestational sac diameter (GSD).
◦ Biparietal diameter (BP).
◦ Biparietal diameter (BP).
◦ Crown rump length (CRL).
◦ Crown rump length (CRL).
◦ Body diameter at the liver (BD).
◦ Body diameter at the liver (BD).
• Species-Specific Formulas:
• Species-Specific Formulas:
◦ Cats: Use a specific formula: mean litter crown rump length (cm) = 0.2423 × gestational age – 4.2165.
◦ Cats: Use a specific formula: mean litter crown rump length (cm) = 0.2423 × gestational age – 4.2165.
• Accuracy: Calculations for dogs are typically accurate within ± 3 days, while cats are accurate within ± 2 days.
• Accuracy: Calculations for dogs are typically accurate within ± 3 days, while cats are accurate within ± 2 days.
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