Page 462 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.1 The female reproductive tr act 437

VetBooks.ir Ultrasound is particularly useful for: during periods of fetal activity. The rate decreases
from 120 bpm at 160 days to 76 +/− 8 bpm in
• Detecting and sexing single or twin pregnancies.
findings are arrhythmias, heart rate above
• Assessing the thickness of the combined the final 30–50 days of gestation. Abnormal
uteroplacental unit and the appearance and 126 bpm (fetal stress) or heart rate below 57 bpm
volume of allantoic and amniotic fluids. (fetal depression, hypoxia). During periods of
• Assessing the position of the fetus within the fetal activity, rate increases of 25–40 bpm are
uterus. considered normal. Fetal heart rate is reduced if
• Measurement of fetal size and gestational age. the mare is sedated during the examination.
• Assessment of the cardiovascular system • Maximum depth of fetal fluid pool. A depth
including fetal heart rate. of around 22 cm is considered normal when
measured by transabdominal ultrasound.
A biophysical profile is built up using a scoring Amniotic fluid – 7.9 +/− 3.5 cm (fetus to amnion),
system derived from the following measurements: allantoic fluid – 13.4 +/− 4.4 cm (amnion to
chorioallantois). Echogenic particles are often
• Combined thickness of uterus and placenta seen in each compartment (amniotic fluid more so
(CTUP). There should be no structural than allantoic fluid) but comparison with previous
distinction detectable between the uterus and examinations is more valuable. Sudden increases in
the allantochorion. Measurements are easily particle density may indicate fetal diarrhoea (fetal
taken by transrectal ultrasonography, just stress), haemorrhage or infection (placentitis).
cranial to the cervix, comfortably within reach • Aortic diameter. Has been shown to correlate to
in most mares. Three measurements should be fetal weight.
taken and an average calculated to avoid any • Uteroplacental contact. Any areas of detachment
inaccurate measurements. The specific region with fluid/exudate visible behind the placenta
of measurement is the ventral uterine wall just either at the cervical pole (transrectal) or base of
cranial to the cervix, and the method involves the uterine horns (transabdominal).
using a rectal ultrasound probe to identify the
cervix together with the caudal placenta and Each of the variables (fetal heart rate, aortic diam-
the probe moved laterally until a blood vessel eter, fetal activity, CTUP, uteroplacental contact
is identified adjacent to the ventral uterine and maximal allantoic fluid depth) can be given a
wall. The measurement is taken from the outer value of 2 for normal and 0 for abnormal. A total
uterine surface to the inner placental surface. value of 8 or less is suggestive of an unfavourable
This is the combined thickness of the uterus and outcome. A maximal score, however, is not an assur-
placenta (CTUP). A CTUP of between 7 and ance of normality, as problems can develop during
13 mm is classed as normal depending on the delivery including premature placental separation,
stage of pregnancy. A helpful approximation dystocia and failure of the chorioallantois to rupture.
for calculating the normal CTUP during Biophysical profiling of the prenatal equine fetus is
pregnancy is: normal CTUP (mm) = 1 + number an area that requires further research if accurate
of months of gestation at time of examination. conclusions are to be made from the findings.
(See Fig. 2.55.) An increased CTUP suggests
placentitis/oedema while a reduced CTUP Fetal electrocardiography
suggests insufficiency. Placental separation may This is a technique that has been used for over
also be seen. 35 years and can, if carefully carried out, docu-
• Fetal activity. Excessive movement may indicate ment the fetal heart rate and the presence of a twin
fetal stress while reduced movement may pregnancy. A normal electrocardiograph machine
indicate fetal compromise (see above). is used and both a mare and fetal trace obtained.
• Fetal heart rate/rhythm is a very sensitive Abnormalities of the fetal heart rate may precede
indicator of fetal well-being. Increases occur fetal death. Electrocardiography should always be