IN-DEPTH: CONDITIONS AND MANAGEMENT OF THE PERIPARTUM MARE Table 2. Selected Normal Fetal Ultrasound Parameters Between 240 Days of Gestation and Term34,39 Stomach


Gestational Age, days


240–270 270–300 300–330 330–360


Peri-Cervical CTUP Breakpoint, mm


7 8


10 12


Combined Fetal Orbital Diameter, mm


57.4  4.9 64.3  2.9 68.1  3.6 70.3  2.7


CTUP, combined thickness of the uterus and placenta.


with a thick, tenacious, mucopurulent exudate that separates the chorionic surface from the endome- trium (Fig. 1B).1,28 Gram-positive, filamentous, branching bacilli, in- cluding Crosiella equi, Amycolatopsis species, and Streptomyces species are found in the exudate and fetal membranes, but not in fetal fluid compart- ments or in the fetus.27,32 In contrast to diffuse placentitis, this condition does not cause fetal sepsis, progresses slowly and may respond to treatment if identified before large portions of the chorioallantois are damaged. Focal placentitis can be diagnosed by identifying the characteristic thickening and sep- aration of the chorioallantois via transabdominal ultrasound. Fetal stress associated with placental insufficiency may also cause bradycardia and alter- ations in fetoplacental hormone production. These and other conditions associated with late-


term pregnancy loss fall into two general categories in regard to disease progression and pregnancy out- come: rapid abortion or prolonged insult. Diffuse placentitis, viral infections, and umbilical torsion frequently result in expeditious abortion of a freshly dead fetus. In those cases, diagnosis is commonly not obtained until after abortion. In contrast, as- cending placentitis, focal placentitis, twin preg- nancy, and placental malfunction may be associated with chronic placental insufficiency and fetal stress prior to abortion, presenting an opportunity for suc- cessful diagnosis and treatment.


4. Diagnostic and Screening Modalities for High-Risk Mares


and consistent across horse breeds.33,34,36–39 Treat- ment based on elevations inCTUPhave been shown in some studies to improve gestational outcome and result in viable and productive offspring.31–37,40–43 The probe is placed just cranial to the cervix and then laterally to visualize a characteristic branch of the middle uterine artery between the bladder/abdominal


Ultrasonographic screening of the CTUP via trans- rectal and transabdominal ultrasound remains the gold standard for preterm diagnosis of placentitis, while detailed ultrasonographic examination of the pregnant uterus is the only reliable means of diag- nosing twins, umbilical torsion or other physical abnormalities preterm. Normal parameters for CTUP are well established


content and the uterus. Placental dysfunction and abortion are associated with increases in the CTUP greater than 8mmbetween 271 and 300 days, 10mm between 301 and 330 days, and greater and 12 mm after 330 days.33,34 In severe cases of placentitis, hy- perechoic debris can be seen between the placenta and the uterus. On transabdominal ultrasonographic ex- amination, the CTUP should be identified in a region with direct or close apposition of the uterus to the body wall and with little folding. Efforts should be made to identify a region of fluid where the amnion is sepa- rated from the chorioallantois to prevent overinterpre- tation of disease. Measurements are made from the external uterine surface, frequently identifiable as a hyperechoic line internal to the body wall, to the hy- poechoic/anechoic allantoic fluid, and should range be- tween 7.1 mm (1.6 mm) and 11.5 mm (2.4 mm) at the ventral aspect of the uterine body.33,34,39 Mea- surement of CTUP should be paired with critical eval- uation of parameters of fetal health, including the presence of a single fetus, fetal activity, fetal fluid characteristics, and fetal heart rate. Specific mor- phologic parameters can be measured to assess appro- priate development for gestational age, as described by Bucca.39 Generally, fetal fluids should be anechoic or hypoechoic, with small amount of free-floating debris depending on the activity level of the foal.43 In late gestation, the amniotic fluid is generally slightly more hyperechoic than the allantoic fluid, which is charac- teristically anechoic with some localized hyperechoic debris visible during fetal activity. The fetus should be in anterior presentation by the end of the ninth month of gestation. The late-term fetal heart rate should be approximately 75 beats per minute, increas- ing by 15–20 beats per minute (bpm) in periods of activity. Distressed fetuses often will have low fetal heart rates (60 bpm) initially, followed by a high heart rate terminally. Selected ultrasonographic pa- rameters during the last 3 months of normal equine gestation are summarized in Table 2. Although ultrasonographic examination repre-


sents a valuable tool for the diagnosis of multiple gestational abnormalities, it has several critical drawbacks: Firstly, transrectal and transabdomi- nal ultrasonography each require specialized equip- ment that not all practitioners have available. Secondly, because parameters are based on subjec- tive placement of the ultrasound probe, they are


AAEP PROCEEDINGS  Vol. 65  2019 129 Measurements, mm


Long Axis 77.5  11.1


97.6  15


102.4  8.7 98.8  14.4


Short Axis 45.1  9.8


58.7  10.8 55.5  87 57.1  9.5


Fetal Aortic Diameter, mm


18.19  1.6 22.25  1.5 24.8  1.4 25.7  1.05


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