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To measure the diameter of the aorta at the caudal border of the heart is a
good indicator of foetal size during late gestation (normal range: 18 – 27 mm)
Abnormal foals with low birth weight have a smaller than normal diameter.
The amniotic membrane is a thin, hyper echoic structure floating within the
foetal fluids and can contain round little cystic structures, which are probably
normal. The membrane can be visualised transrectally and trans abdominally.
Foetal fluids; there are 4 areas within the uterus (right and left cranial and
caudal) where one can try to check the depth of the allantoic and amniotic
fluid, with normal ranges of 14 ± 5 cm and 8 ± 4 cm respectively. As of the 4th
month of gestation, the allantoic and amniotic fluids contain a moderate
amount of free-floating particles (vernix). The hippomane, can be seen in the
allantoic fluid as a floating elongated layered structure.
The CUPT is assessed by trans rectal ultrasound exam and is ideally
performed approximately 10 cm ventral from the internal os of the cervix with
the view to exclude the presence of ascending placentitis. In normal
pregnancies it ranges from a minimum of 7.1 ± 1.6 mm and a maximum of 11
± 2.4 mm. When the CUPT is over 17.5 mm it is consistent with the presence
of placentitis. The CUPT can also be measured on different other spots of the
uterus via trans abdominal ultrasound but it is impossible to overlook the
uterine wall completely.
Proper foetal gender determination can be performed via trans rectal U/S
exam around 60 days post-ovulation and via trans abdominal U/S exam as of
120 days post ovulation. The foetal gonads are elliptically shaped and occupy
the ventrocaudal abdomen, below each kidney, with an oblique orientation,
divergent cranially. They are not too far located from the bladder and the
urachus. The male foetal gonads appear uniformly echogenic, with a central
hyper echoic line running on the long axis, believed to correspond to the
location of the testicular vein, in postnatal life. Colour Doppler ultrasonography
of the foetal gonad clearly identifies the course of the testicular vein in the
male, while a strong cortical pattern is evident in the female foetus. The
epididymis can sometimes be visualized on the dorsolateral aspect of each
gonad. The mammary gland can be visualized as a triangular to trapezoidal
structure. In the female foetus with nipples commonly identified as two hyper
echoic protrusions on the cranial margin of the mammary gland. The equine
foetal vulva is in general difficult to be seen on U/S. The clitoris is identified as
a hyper echoic, caudal, ‘teardrop’ structure, bulging out, where the buttocks
meet. In the equine filly foetus, gonads present a structural differentiation
between cortex and medulla that translates into substantial echo texture.
To detect developmental abnormalities during late gestation such as:
microphthalmus, hydrocephalus, small and large intestinal segmental atresia
and renal abnormalities, calcified remnants of the vitelline sac.
Regular breathing movements may be observed in all foetuses as of 7 months
of gestation, and becomes easier when the diaphragm is visualised.
The non-pregnant horn can show a thickened folded appearance, which is
completely normal and could be mistaken for an utero-placental thickening.
The lumen is relatively small but can increase to make place for larger volume
of fluids.
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
254