Diagnosis of pregnancy is usually performed by ultrasound examination
of the uterus at 12 to 14 days after ovulation. The particular situation and vet preferences dictate the timing for further examinations.
Most veterinarians recommend rechecking the pregnancy at 21 to 25, 30 and 60 days post-ovulation, since most early embryonic losses occur prior to 45 days in mares. Late pregnancy checks by palpation or ultrasound can be performed when the mare is vaccinated or in case of health problems or complications.
At each pregnancy check, your veterinarian may choose to perform a complete physical examination to ensure that your mare is in good health and body condition. The udder should be checked periodically for abnormalities or for timely development towards lactation. Mild increases in udder size may be noticed 4 to 6 weeks prior to the due date, mostly due to fluid accumulation or edema; however, glandular development and marked increases in udder size are not usually noted until 2 to 3 weeks prior to the foaling date. Premature udder development and/or lactation are usually a sign of impending abortion.