Amniotic fluid function
Cushion for fetus movement
Stabilize the temp.
Lung mature
Amniotic formation
1st trimester: 35mL from maternal plasma
2nd & 3rd trimester: Increase due to fetal urine –> necessary to expand the lungs. Can reach 800-1200 mL
Amniotic composition
- Fetal respiratory movement: lecithin, sphingomyelin, phosphatidylglycerol –> index of lung maturity.
- Sloughed fetal cells: from fetal skin, digestive system, urinary tract –> cytogenetic analysis
- Biochemical substances: bilirubin, lipids, enzyme, electrolytes, protein, hormones.
- Neural tube defects: CSF of fetal present in amniotic fluid
- Urine production: creatinine, urea, uric acid
Amniotic collected
Amniocentesis: through ultrasound, transabdominal, and vaginal amniocentesis
V: Max 30mL (1st 2-3mL contaminated with maternal plasma)
Amniotic indicator in 15-18 weeks
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
Amniotic indicator in 20-42 weeks
Fetal lung maturity
Fetal distress
HDN caused by Rh blood type incompatibility
Infection
Sample handling
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
Amniotic appearance
- 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
Differentiate amniotic and urine
Why:
- Possible leakage
- Accidental puncture
How:
- Chemical analysis of creatinine, urea, glucose, protein
- Fern test
Amniotic vs Urine - Chemical
- Amniotic:
- high glucose, protein
- creatinine: less than 3.5 mg/dL
- urea: less than 30 mg/dL - Urine
- creatinine: 10 mg/dL
- urea: ~ 300 mg/dL
Fern test
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)
Bilirubin vs Fetal distress
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.
Testing method for bilirubin
Spectrophotometry
Normal sample: steadily declining from 350nm to 580nm
Abnormal sample: has a peak at 450nm
Bilirubin - toxic for the fetal
Neurotoxin leads to brain damage, tissue, seizure, severe anemia, enlarged liver, spleen, heart, organ failure and death
Lecithin/Sphingomyelin Ratio
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
Phosphatidylglycerol test
- 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
Lamellar Body Count test
- 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.
Alpha-fetoprotein (AFP)
- 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
Acetylcholinesterase (AchE)
- 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)
