••• Chapter 18^ Amniotic Fluid^189
❍ What is the most common cause of oligohydramnios?
Premature rupture of the membranes.
❍ What serious complications are associated with oligohydramnios occurring before 22 weeks?
- Pulmonary hypoplasia.
- Amniotic band syndrome.
- Fetal compression syndrome.
❍ What is Potter sequence?
A collection of physical features in addition to pulmonary hypoplasia resulting from oligohydramnios and fetal
compression in utero. Physical features include skeletal malformation, typical facies (flattened nose, recessed chin,
prominent epicanthal fold, low set ears), and cardiovascular malformations.
❍ What is the most common cause of Potter sequence?
Bilateral renal agenesis.
❍ Why is the second trimester oligohydramnios associated with pulmonary hypoplasia?
Amniotic fluid inspired at regular intervals, and the distending force it creates, is needed for proper terminal
alveolar development.
❍ What is the most likely cause of second trimester oligohydramnios in the absence of ruptured membranes?
Congenital anomalies.
❍ What is the most likely cause of third trimester oligohydramnios in the absence of ruptured membranes?
Intrauterine growth restriction.
❍ What is the mechanism of oligohydramnios in fetuses with intrauterine growth restriction?
Chronic hypoxia resulting in shunting of fetal blood flow from the kidneys, thereby decreasing glomerular
filtration rate (GFR) and decreasing fetal urine output.
❍ A large bladder in the presence of oligohydramnios is associated with what cause for the oligohydramnios?
Urethral obstruction.
❍ If a fluid-filled bladder is seen on ultrasound, what potential congenital abnormality is ruled out as a cause
of oligohydramnios?
Bilateral renal agenesis.
❍ What medications can cause oligohydramnios?
Prostaglandin synthetase inhibitors and ACE inhibitors.
❍ What is the mortality rate of oligohydramnios in the second trimester?
Fetal mortality rate has been reported as high as 80% to 90%. The earlier the diagnosis, the worse the prognosis.