Oligo/ Polyhydramnios

Question 1

Oligohydramnios definition

Answer 1

a. Amniotic fluid volume less than expected for gestational age
b. USS features
i. Single deepest pocket <2cm
ii. AFI <5cm

Question 2

Oligo pathophysiology

Answer 2

a. Volume of amniotic fluid determined by volume flowing into and out of the amniotic sac
b. Influenced by: foetal urination, lung fluid, swallowing

Question 3

Oligo aetiology

Answer 3

a. Maternal factors
i. Uteroplacental insufficiency eg preeclampsia, HTN, nephropathy, thrombophilia, collagen vascular disease
ii. Medications – ACEi, prostaglandin synthetase inhibitors
b. Placental factors
i. Abruption
ii. Twin to twin transfusion (ie, twin polyhydramnios-oligohydramnios sequence)
iii. Placental thrombosis/infarction
c. Foetal factors
i. Chromosomal abnormalities
ii. Congenital abnormalities of renal tract
1. Bilateral renal agenesis
2. Atresia of ureter/urethra  hydronephrosis
3. Renal hypoplasia
4. Polycystic kidney disease
iii. Growth restriction
iv. Foetal demise
v. Post-term pregnancy
vi. Ruptured membranes

Question 4

Oligo aetiology based on trimester

First trimester

Answer 4

1. Rare, usually unclear cause, pregnancy usually aborts
2. This is when foetal urine production starts (5-7 weeks)
   ii. Outcomes
3. Usually abortion

Question 5

Oligo aetiology based on trimester

Second trimester

Answer 5

i. Aetiology
1. Begins to swallow amniotic fluid
2. Disorders related to fetal renal/urinary systems
a. Cystic renal disease
b. Obstructive lesions – posterior urethral valves, urethral atresia, prune belly syndrome)
3. Maternal and placental causes common  leakage
ii. Outcomes – often poor
1. IUGR
2. Preterm delivery
3. Neonatal death
4. Cord compression – asphyxia
5. Anatomical and functional abnormalities – skeletal deformations, contractures, pulmonary hypoplasia
iii. Pulmonary hypoplasia
1. Small lungs with relatively normal compliance, high pulmonary vascular resistance, reduced pulmonary blood flow, cardiac dysfunction
2. 70-90% mortality
3. Less common when >26/40 (end of canalicular stage of lung development – acinar structures less sensitive external pertubations)

Question 6

Oligo aetiology based on trimester

Third trimester

Answer 6

1. PPROM
2. Uteroplacental insufficiency d/t pre-eclampsia, vascular diseases
3. Post-term
   ii. Prognosis
4. Cord compression
5. Uteroplacental insufficiency
6. Meconium aspiration

Question 7

Potter Sequence

Answer 7

Caused by oligohydramnios secondary to renal agenesis or other renal anomalies resulting in reduced fetal urine output production resulting in oligohydrmanios
• Features
o Positional limb deformities – club feet, hip dislocation
o Facial appearance - pseudoepicanthus, recessed chin, posteriorly rotated, flattened ears, and flattened nose
o Pulmonary hypoplasia

Question 8

Polyhydramnios definition

Answer 8

a. Excess volume of amniotic fluid
b. USS features
i. Single deepest pocket >=8cm
ii. AFI >=24cm

Question 9

Poly pathophysiology

Answer 9

a. Volume of amniotic fluid determined by volume flowing into and out of the amniotic sac
b. Influenced by: foetal urination, lung fluid, swallowing

Question 10

Poly pathophysiology

Answer 10

a. Maternal factors
i. Diabetes
b. Fetal factors
i. Fetal structural anomaly
ii. Fetal chromosomal abnormality (eg. T18)
iii. High fetal cardiac output (any condition causing anaemia)
iv. TTTS
v. Neuromuscular disorders
vi. Fetal Bartter syndrome

Question 11

Polyhydramnios clinical significance

Answer 11

a. Maternal respiratory compromise
b. Preterm labor, premature rupture of membranes (PROM), preterm delivery
c. Fetal malposition
d. Macrosomia (potentially leading to shoulder dystocia)
e. Umbilical cord prolapse
f. Abruption upon rupture of membranes
g. Longer second stage of labor
h. Postpartum uterine atony

Question 12

Management of polyhydramnios

Answer 12

a. Controversial

b. Amnioreduction