Amniotic Fluid

Question 1

Amniotic fluid function

Answer 1

Cushion for fetus movement
Stabilize the temp.
Lung mature

Question 2

Amniotic formation

Answer 2

1st trimester: 35mL from maternal plasma

2nd & 3rd trimester: Increase due to fetal urine –> necessary to expand the lungs. Can reach 800-1200 mL

Question 3

Amniotic composition

Answer 3

1. Fetal respiratory movement: lecithin, sphingomyelin, phosphatidylglycerol –> index of lung maturity.
2. Sloughed fetal cells: from fetal skin, digestive system, urinary tract –> cytogenetic analysis
3. Biochemical substances: bilirubin, lipids, enzyme, electrolytes, protein, hormones.
4. Neural tube defects: CSF of fetal present in amniotic fluid
5. Urine production: creatinine, urea, uric acid

Question 4

Amniotic collected

Answer 4

Amniocentesis: through ultrasound, transabdominal, and vaginal amniocentesis
V: Max 30mL (1st 2-3mL contaminated with maternal plasma)

Question 5

Amniotic indicator in 15-18 weeks

Answer 5

Mother at 35 yrs and older
3 or more miscarriages
Check for chromosome abnormalities ( trisomy 21) or other abnormal arrangement
Genetic disease, metabolic disorder
Elevated maternal serum alpha-fetoprotein
Neural tube disorder –> spina bifida

Question 6

Amniotic indicator in 20-42 weeks

Answer 6

Fetal lung maturity
Fetal distress
HDN caused by Rh blood type incompatibility
Infection

Question 7

Sample handling

Answer 7

Ice transport and refrigerated for a fetal lung test
Protect from light for bilirubin test
Room/37 temp (prolong cell viability and integrity) for cytogenetics and microbial test

Question 8

Amniotic appearance

Answer 8

• Normal: Colorless, pale yellow with slight to moderate turbid
• Blood streaked: trauma tap, abdominal trauma, intra-amniotic hemorrhage (test to distinguish maternal/fetal RBC)
• Yellow: newborn hemolytic disease
• Dark green: meconium
• Dark red-brown: fetal death

Question 9

Differentiate amniotic and urine

Answer 9

Why:

• Possible leakage
• Accidental puncture

How:

• Chemical analysis of creatinine, urea, glucose, protein
• Fern test

Question 10

Amniotic vs Urine - Chemical

Answer 10

1. Amniotic:
   - high glucose, protein
   - creatinine: less than 3.5 mg/dL
   - urea: less than 30 mg/dL
2. Urine
   - creatinine: 10 mg/dL
   - urea: ~ 300 mg/dL

Question 11

Fern test

Answer 11

Cervical mucus specimen used to determine membrane leakage.
Procedure: Swab the cervical mucus –> air dry on the slide
–> Normal: no crystal seen
–> Membrane leakage: a leaf, fern-like crystallization seen indicates amniotic fluid (Sodium chloride and other minerals)

Question 12

Bilirubin vs Fetal distress

Answer 12

Normal: no detectable bilirubin
High amount: hemolytic disease of a newborn (due to the RH conflict btw mom and baby)
* Bilirubin incre due to incre hemolysis in the fetus and immature liver that is unable to process the load of bilirubin.

Question 13

Testing method for bilirubin

Answer 13

Spectrophotometry
Normal sample: steadily declining from 350nm to 580nm
Abnormal sample: has a peak at 450nm

Question 14

Bilirubin - toxic for the fetal

Answer 14

Neurotoxin leads to brain damage, tissue, seizure, severe anemia, enlarged liver, spleen, heart, organ failure and death

Question 15

Lecithin/Sphingomyelin Ratio

Answer 15

Lecithin: surfactant that up the alveolar lining
Sphingomyelin: lipid produced after 26 weeks of gestation
L/S = 2.0-2.5: Normal fetal lung maturity
L/S < 2.0: Immature fetal lung development
* Tested by Thin Layer Chromatography

Question 16

Phosphatidylglycerol test

Answer 16

• Lung surfactant lipid can be detected after 35 wks of gestation
• Combine with L/S to get a full picture of lung maturity
• Tested by TLC or Immunologic agglutination test

Question 17

Lamellar Body Count test

Answer 17

• Storage form of lung surfactant: packed layers of phospholipid
• LB in amniotic ~ phospholipid in fetal lung
• Tested by platelet channels of an automated hematology analyzer
• Sample can’t be contaminated with blood, meconium, or mucus. Sample can’t be frozen.

Question 18

Alpha-fetoprotein (AFP)

Answer 18

• Major protein made by the fetal liver (~18 wks)
• Normal level: depend on the week of gestation
• 2x median = abnormal
• High level: fetal neural tube defect, such as spina bifida, anencephaly

Question 19

Acetylcholinesterase (AchE)

Answer 19

• Tested when AFP is elevated as more specific for neural tube defects
• Enzyme hydrolyzes the neurotransmitter- acetylcholine.
• Sample can’t be contaminated with blood (cause false positive)