9.2c Biochemical Monitoring Techniques

Question 1

Biochemical Assessment

Answer 1

• 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)

Question 2

Amniocentesis

Answer 2

• 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.

Question 3

Complications of Amniocentesis

Answer 3

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

Question 4

INDICATIONS FOR AMNIOCENTESIS

Question 5

Genetic Concerns

Answer 5

• 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

Question 6

Fetal Lung Maturity

Answer 6

• 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)

Question 7

Fetal Hemolytic Disease

Answer 7

• No longer used for this (used to be used to detect isoimmunization)
• Doppler Velocimetry is now used to determine fetal anemia and isoimmunized pregnancies

Question 8

Chorion Villus Sampling (CVS)

Answer 8

• 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

Question 9

Percutaneous Umbilical Blood Sampling (PUBS)

Answer 9

• 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.

Question 10

Maternal Assays

Question 11

A-Fetoprotein

Answer 11

• 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

Question 12

AFP

Answer 12

• Amniotic fluid AFP is a diagnostic test for NTD

- Maternal Serum ATD is only a screening for possible NTD

Question 13

MSAFP (Maternal Serum AFP)

Answer 13

• 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

Question 14

Multi Marker Screens

Answer 14

• 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

Question 15

Trisomy 21 (down syndrome)

Answer 15

• 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

Question 16

Trisomy 18 and 13

Answer 16

• hCG and PAPP-A levels will be lower than normal

Question 17

Disintegrin and Metalloproteinase 12 (ADAM12)

Answer 17

• Biochemical markers measured in 8-10 weeks of gestation
• ## Glycoproteins synthesized by placenta and secreted during pregnancy

Question 18

QUAD Test for Trisomy 21 and 18

Answer 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)

Question 19

Trisomy 21 second trimester

Answer 19

• MSAFP and Unconjugated estriol is lower

- hCG and Inhibin are elevated

Question 20

COOMBS Test

Answer 20

• 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

Question 21

Aneuploidy

Answer 21

• Missing Chromosomes
• Determined with cfDNA Test (Cell-Free DNA)
• Done with noninvasive sample of maternal blood

Question 22

AMNIOTIC FLUID ANALYSIS

Answer 22

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