33. Amniotic fluid and its disorders. Polyhydramnios and oligohydramnios

Question 1

what is the role of the amniotic fluid?

Answer 1

(1) Cushion the fetus
(2) Prevent adherence of the fetus to the amnion
(3) Transport medium for nutrients and metabolites
(4) Antibacterial properties
(5) Provides the necessary fluid, space, and growth factors to permit normal development of the fetal lungs, musculoskeletal, and gastrointestinal systems

Question 2

how much average amniotic fluid is produced by the fetus?

Answer 2

500-700 mL amniotic fluid per day.
Amniotic fluid volume increases until 34-36 weeks, after which the volume decreases

Question 3

what is the amniotic fluid derived from in the 1st trimester?

Answer 3

fetal and maternal compartments
Water and solutes freely traverse fetal skin and may diffuse through the amnion and
chorion

Question 4

what is the amniotic fluid derived from in the 2nd trimester?

Answer 4

the fetus contributes to amniotic fluid volume and composition almost exclusively through urination, cause the fetal skin becomes keratinized, making it impermeable to further diffusion.

plus the fetal lungs secrete amniotic fluid

Question 5

what is the composition of the amniotic fluid in the 1st trimester?

Answer 5

dialsyate
identical to the fetal and maternal plasma, but with a lower protein concentration.

Question 6

how is amniotic fluid eliminated?

Answer 6

by three mechanisms: fetal swallowing, removal by the
respiratory tract, and osmotic exchange at the chorionic plate.

Question 7

what is the Single deepest pocket (SDP)?

Answer 7

The vertical dimension in centimeters of the largest pocket of amniotic fluid not persistently containing fetal extremities or umbilical cord
also known as maximum vertical pocket (MVP).

Question 8

how is the amniotic fluid index calculated?

Answer 8

by dividing the uterus into 4 quadrants
the sum of these measurements is the AFI.

Question 9

what is Oligohydramnios?

Answer 9

Defined as amniotic fluid volume that is less than expected for gestational age.

Question 10

when should oligohydramnios first be suspected?

Answer 10

based on size/date discrepancy or may be detected on an US examination performed for other indication.

Question 11

potential etiologies for Oligohydramnios

Answer 11

• Congenital anomalies of the urinary tract: renal agenesis, polycystic kidney disease, posterior urethral valve, obstructive uropathy
• Uteroplacental insufficiency: preeclampsia, HTN, thrombosis, collagen vascular disorders
• Twin-to-twin transfusion syndrome (TTTS) – donor embryo
• Drugs: ACE inhibitors, prostaglandins synthesis inhibitors, trastuzumab
• ROM (results in acute-onset oligohydramnios)

Question 12

what should be done after diagnosing oligohydramnios?

Answer 12

• Rule-out PROM
• Maternal history and physical examination
• US to assess fetal anomalies and potential IUGR
• Fetal genetic studies
• Maternal serum alpha-fetoprotein (AFP)
• MRI

Question 13

management of Oligohydramnios

Answer 13

1. Amnioinfusion
2. Target underlying etiology.
3. Maternal hydration therapy.
4. Delivery if close to term.

Question 14

how is amnioinfusion done for oligohydramnios?

Answer 14

Under US guidance, a needle is inserted through the uterine wall and amniotic cavity.
Isotonic fluid (normal saline or Ringer’s lactate) is infused until the volume of amniotic fluid is normalized. The procedure may be repeated regularly if oligohydramnios recurs (serial amnioinfusion).

Question 15

complications of oligohydramnios

Answer 15

1. Intrauterine growth restriction (IUGR); due to diminished mobility of the fetus.
   2.Birth complications (umbilical cord compression).
   3.Potter sequence:
   Oligohydramnios → compression of the developing fetus → limb deformities, facial anomalies (low-set ears, retrognathia, flattened nose), compression of chest and lack of amniotic fluid aspiration into fetal lungs → pulmonary hypoplasia (cause of death).

Question 16

what is polyhydramnios?

Answer 16

Defined as amniotic fluid volume that is excessive to gestational age

Question 17

how does polyhydramnios present?

Answer 17

with a uterine size that is large for gestational age or as an incidental finding on a prenatal ultrasound examination.

usually asymptomatic, but persistent shortness of breath, uterine irritability and contractions, and abdominal discomfort can occur when uterine distention is severe

Question 18

potential etiologies for polyhydramnios

Answer 18

• Idiopathic (in up to 40% of cases)
• Gestational diabetes: glucose acts as an osmotic diuretic in the fetus
• Gastrointestinal tract abnormalities: esophageal atresia, tracheoesophageal fistula, duodenal atresia.
• Anencephaly: impaired swallowing of amniotic fluid, leakage of cerebrospinal fluid
• Twin-to-twin transfusion syndrome (TTTS) – recipient embryo
• Fetal anemia, hydrops: high output heart failure

Question 19

after polyhydramnios is diagnosed, what tests can be done?

Answer 19

1. Maternal history and physical examination
2. US to assess fetal anomalies
3. MCA-PSV (middle cerebral artery peak systolic velocity – assess fetal anemia)
4. Fetal genetic studies
5. Screen for maternal diabetes

Question 20

management of polyhydramnios

Answer 20

1. Decompression amniocentesis (amnioreduction) to normalize fluid volume.
2. Target underlying etiology.
3. Timing and method of delivery depend upon the etiology and severity of polyhydramnios.

Question 21

when is amnioreduction indicated?

Answer 21

patients with severe polyhydramnios: indicative findings on US (AFI > 35 cm or SDP > 16 cm) and clinical symptoms (shortness of breath and/or abdominal discomfort).

Question 22

complications of polyhydramnios

Answer 22

• Maternal respiratory compromise
• Preterm labor
• PROM, PPROM
• Fetal malposition
• Abruptio placentae
• Umbilical cord prolapse
• Postpartum uterine atony