ultrasound diagnosis of fatal anomalies

OLIGOHYDRAMNIOS
Oligohydramnios
Definition: Decrease in the volume of amniotic
fluid; oligohydramnios is diagnosed if the
diameter of the largest amniotic fluid depot is
below2 cm, or if the amniotic fluid index lies
below5.1 cm. The amniotic fluid index (AFI) is
defined as the sum of the largest vertical diameters
of the amniotic fluid depots measured in all
four quadrants of the uterus. The normal average
volume of the amniotic fluid at 16 weeks of gestation
is 250 mL; it increases to 800 mL at 28
weeks and further to 1000 mL at 38 weeks,
decreasing slightly to 800 mL at 40 weeks.
Incidence: Oligohydramnios is diagnosed in
0.5–4.0% of all pregnancies, depending on howit
is defined.
Teratogen: Indomethacin.
Etiology: Reduced urine production, premature
rupture of the membranes.
Ultrasound findings: The reduced amount of
amniotic fluid makes ultrasound examination
difficult. Renal diseases, such as bilateral renal
agenesis, cystic anomalies of the kidneys, dysplasia,
and obstructive uropathy may be causative
factors. In addition, severe growth restriction
and premature rupture of the membranes
may also be considered. Oligohydramnios over a
long period of time causes club feet and other
anomalies.
Clinical management: Amnioinfusion is carried
out in severe cases to allowsonographic diagnosis
of fetal anomalies and to exclude rupture of
the membranes. In the later stages of the second
trimester and in the third trimester, Doppler
flowimaging of the fetal and maternal vessels is
used to detect signs of placental insufficiency.
Prognosis: This is favorable if oligohydramnios
develops late in pregnancy. Detection of oligohydramnios
in the first trimester or early second
trimester is a bad sign and is an indication of
severe underlying anomalies. In these cases, the
prognosis is poor due to pulmonary hypoplasia
secondary to oligohydramnios.
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