Oligohydramnios

Question 1

Definition

Answer 1

AFI < 5, Borderline is 5-8cm

Evidence supports use of single deepest pool <2cm, or severe <1cm

Question 2

What determines amniotic fluid level?

Answer 2

• fetal urination
• lung fluid
• swallowing
• some degree of homeostatic mechanisms of membrane (however better with preventing polyhydramnios)

Question 3

Likely causes of oligohydramnios in second trimester?

Answer 3

• if oligo presenting likely to be fetal urinary/ kidney issues/ fetal anomaly
  o renal agenesis
  o obstructive uropathies
• maternal placental factors
• PPROM
• Oligo + fetal anomalies also likely to have raised AFP (carries poor prognosis)

Question 4

Likely causes of oligohydramnios in third trimester?

Answer 4

• PPROM/PROM
• Placental insufficiency
• Maternal hydration
• Prostaglandin synthase inhibitors e.g. indomethacin, NSAIDS

Question 5

Effect of oligohydramnios on fetus

Answer 5

• pulmonary hypoplasia if very preterm
• umbilical cord compression
• poor apgars
• meconium liqour

Question 6

What is the purpose of amniotic fluid?

Answer 6

• Gives fetus the freedom to move about, thus enabling musculoskeletal (muscle and bone) development.
• Prevents compression on the umbilical cord
• When the fetus swallows the amniotic fluid, this helps it to develop its gastrointestinal tract.
• The fetus inhales and exhales the fluid, which stimulates lung development.
• Acts as a barrier against fetal infection of the intra-amniotic environment, while it also offers protection against any blows, for example if the mother falls.

Question 7

How is amniotic fluid produced?

Answer 7

During the first trimester of pregnancy, the main component of amniotic fluid is from transfer across amniotic membranes by osmotic and hydrostatic pressure from maternal plasma. It mostly contains water at this time.

After 16 weeks the fetal kidneys start to produce urine, and the baby is the main producer of amniotic fluid. Fetal urine and fluid excreted from its lungs also contributing to the fluid.

Amniotic fluid volume increases to around 800ml at 32-34wks and plateaus. It gradually decreases from term and may be down to 400ml at 42 weeks.

Question 8

When is the peak of amniotic fluid?

Answer 8

32-34 weeks of gestation. After 36 weeks of gestation, the volume declines naturally.