9.2c Biochemical Monitoring Techniques Flashcards
Biochemical Assessment
- Biological assessment of chromosomes in exfoliated cells
- Chemical determinations such as L/S ratio, PG, and LBC
- Procedures to obtain include amniocentesis, PUBS, CVS, and maternal blood sampling
PUBS (Percutaneous Umbilical Cord Sampling)
CVS (Chorionic Villus Sampling)
Amniocentesis
- Can be done after the 14th week (sample of amniotic fluid)
- Used to find genetic disorders like neural tube defects, pulmonary maturity, and rarely fetal hemolytic disease)
- Can detect AFP (A-fetoprotein)
- High AFP levels confirm NTD (spina bifida, anencephaly, omphalocele)
- High AFP levels are caused by increased leakage of cerebrospinal fluid or abdominal fluid into amniotic fluid.
Complications of Amniocentesis
Mother - Leakage of amniotic fluid, fetal hemorrhage which can cause isoimmunization, infection, labor, placental abruption, amniotic fluid embolism (anaphylactoid syndrome)
Fetal - Death, hemorrhage, infection (amnionitis), injury from needle
INDICATIONS FOR AMNIOCENTESIS
Genetic Concerns
- Maternal age 35+
- Paternal age 40-50
- Carriers of genetic disorders (sickle cell, cystic fibrosis)
- History of babies with structural defects
- History of babies with chromosomal abnormalities
Fetal Lung Maturity
- Determines L/S Ratio and PG Lung Immaturity
- LBC is a test to detect fetal pulmonary maturity
(Lamellar bodies are surfactant particles secreted by type 2 pneumocytes)
(Lamellar bodies in amniotic fluid increases with fetal pulmonary maturity)
(LBC is used with L/S Ratio and PG Test to determine lung maturity)
Fetal Hemolytic Disease
- No longer used for this (used to be used to detect isoimmunization)
- Doppler Velocimetry is now used to determine fetal anemia and isoimmunized pregnancies
Chorion Villus Sampling (CVS)
- Popular genetic testing technique during the 1st trimester (placental biopsy)
- Similar to amniocentesis but cannot be used for maternal serum marking because it does not draw amniotic fluid
- Is just as accurate as amniocentesis in the 2nd trimester with no greater risks
- Can be done between 10-13 weeks and involves removal of a small piece of placenta through transcervical or transabdominal
Percutaneous Umbilical Blood Sampling (PUBS)
- Also called cordocentesis or funipuncture
- Used for fetal blood sampling and transfusions
- Done by inserting a needle directly into fetal umbilical vein
- Used to evaluate findings of amniocentesis or CVS when blood is needed to determine the mutation
- Can also check for anemia, thrombocytopenia and infection
COMPLICATION
- Bleeding from cord puncture (most common)
- Transient fetal bradycardia
- Can rarely cause amnionitis or transplacental hemorrhage in mom.
Maternal Assays
A-Fetoprotein
- Used as a screening tool for NTD (Neural Tube Defects)
- Recommended for all women
- Risks for NTD include history of it, folic acid deficiency, pregestational diabetes, teratogen exposure
- AFP is made in the fetal GI Tract and liver
- Increasing levels can be detected at 7 weeks of gestation
AFP
- Amniotic fluid AFP is a diagnostic test for NTD
- Maternal Serum ATD is only a screening for possible NTD
MSAFP (Maternal Serum AFP)
- Can be done between 15-20 weeks (16-18 is ideal)
- If MSAFP levels are elevated, ultrasound should be preformed to evaluate gestational age, presence of single pregnancy, and other causes of elevated levels
Multi Marker Screens
- Screens for chromosomal abnormalities such as Trisomy 21 (down syndrome)
- Can be done in first trimester 11-14 weeks
- Measures 2 biochemical markers (PAPP-A and hCG). Also evaluates NT (Nuchal Translucency)
- These tests are screenings and not diagnostics. Positive result means “risk” not definite
Trisomy 21 (down syndrome)
- hCG levels and NT measurement will be higher than normal in the first trimester
- PAPP-A (Pregnancy associated plasma protein A) levels will be lower than normal
- Decreased ADAM 12 levels
- Can also be detected with fetal nasal bone during the first trimester
Trisomy 18 and 13
- hCG and PAPP-A levels will be lower than normal
Disintegrin and Metalloproteinase 12 (ADAM12)
- Biochemical markers measured in 8-10 weeks of gestation
- ## Glycoproteins synthesized by placenta and secreted during pregnancy
QUAD Test for Trisomy 21 and 18
- Its the only test used in the second trimester
- Preformed at 15-21 weeks
MEASURES
- MSAFP
- Unconjugated Estriol
- hCG
- Inhibin (helps detect down syndrome)
Trisomy 21 second trimester
- MSAFP and Unconjugated estriol is lower
- hCG and Inhibin are elevated
COOMBS Test
- Screens for rH incompatibility
- Detects antibodies that can put fetus at harm
- If maternal antibodies are greater than 1:8, amniocentesis is required to determine bilirubin in amniotic fluid which determines the severity of fetal hemolytic anemia
- Middle Cerebral Artery Doppler can also determine fetal hemolytic anemia
Aneuploidy
- Missing Chromosomes
- Determined with cfDNA Test (Cell-Free DNA)
- Done with noninvasive sample of maternal blood
AMNIOTIC FLUID ANALYSIS
Lung Profile - Fetal Lung Maturity
L/S Ratio - Should be 2:1, detects fetal lung maturity
Phosphatidylglycerol - Detects Fetal Lung Maturity if it is present
LBC - >50,000 detects Fetal Lung Maturity
Creatinine - > 2mg/dL indicates >36 week gestational age
Lipid Cells - >10% indicates >35 week gestational age
AFP - High levels after 15 weeks indicates NTD (Neural Tube Defects)
Osmolarity - Declines after 20 weeks of gestation and indicates advancing gestational age
