Amniotic Fluid Analysis - Lecture 8

A set of 100 vocabulary-style flashcards covering amniotic fluid analysis, including composition, collection, pathology, and fetal lung maturity testing based on the lecture notes.

Amnion

The membrane that contains the amniotic fluid and protects the fetus.

Amniotic Fluid

A fluid surrounding the fetus that is initially produced by the amnion and placenta and later includes fetal contributions.

Amniotic fluid volume (12 weeks)

\n25\,mL\text{ to }50\,mL\n

Amniotic fluid volume (37 weeks)

\n800\,mL\text{ to }1200\,mL\n

Amniotic fluid volume (20 weeks)

\n350\,mL\n

Amniotic fluid volume (40 weeks)

\n600\,mL\n

Amniocentesis

The collection of amniotic fluid transabdominally or vaginally under ultrasound guidance.

Amniocentesis timing (genetic disorders)

Performed early in gestation between $15\text{ and }18\text{ weeks}.$

Amniocentesis timing (lung maturity)

Performed late in gestation between $32\text{ and }42\text{ weeks}.$

Fetal distress monitoring

Assessment that can be performed via amniocentesis at any time during pregnancy.

Collection volume

Typically $10\,mL\text{ to }20\,mL$ of fluid collected into numbered syringes.

Amniotic fluid transport

Transported immediately to the lab at room temperature in sterile plastic containers.

Light sensitivity

Amniotic fluid must be protected from light because bilirubin is very light sensitive.

Normal amniotic fluid appearance

Colorless or pale yellow and somewhat turbid.

Yellow or amber fluid

An abnormal color indicating the presence of bilirubin.

Green fluid

An abnormal color indicating the presence of meconium from the fetal intestine.

Pale pink to red fluid

An abnormal color indicating the presence of blood or hemoglobin.

Late pregnancy turbidity

Increased cloudiness due to higher concentrations of fetal cells, hair, and vernix.

Vernix

A waxy substance from fetal skin found in amniotic fluid in late pregnancy.

Amniotic fluid proteins

Includes albumins and globulins.

Amniotic fluid lipids

Includes phospholipids, cholesterol, and lecithin.

Amniotic fluid carbohydrates

Predominantly glucose.

Dermal fibroblasts

Cells in the fluid that grow well in culture and are frequently used for karyotyping.

Karyotyping

The process used for genetic counseling and identifying chromosomal abnormalities.

Alpha fetoprotein (AFP)

A glycoprotein produced by the yolk sac (1st trimester) and fetal liver (2nd trimester).

Yolk sac

The site of large-scale alpha fetoprotein production during the first trimester.

Fetal liver

The primary site of alpha fetoprotein production during the second trimester.

AFP pathology (increase)

Associated with open neural tube defects, exomphalos, and Turner's syndrome.

Anencephaly

An open neural tube defect characterized by the absence of a major portion of the brain and skull.

Spina bifida

An open neural tube defect where the spinal cord fails to develop properly.

Exomphalos

A condition where abdominal organs protrude into the umbilical cord, associated with increased AFP.

Turner's syndrome

A genetic condition that can lead to increased levels of alpha fetoprotein.

Oligohydramnios

A condition where the amniotic fluid volume is less than expected for gestational age.

Deepest vertical pocket (Oligohydramnios)

An ultrasound diagnostic criterion defined as $< 2\,cm$.

Idiopathic oligohydramnios

The most common cause of mild cases of low amniotic fluid volume.

Bilateral renal agenesis

A fetal anomaly leading to oligohydramnios because the kidneys do not develop.

Urethral obstruction

A fetal anomaly that prevents urination, contributing to oligohydramnios.

Placental insufficiency

A maternal condition that can cause reduced amniotic fluid volume.

Postterm pregnancy

Pregnancies lasting longer than $42\text{ weeks}$ of gestation, which are a risk factor for oligohydramnios.

Potter sequence

Complications of oligohydramnios including pulmonary hypoplasia, craniofacial abnormalities, and limb anomalies.

Pulmonary hypoplasia

Underdevelopment of the lungs, often a complication of oligohydramnios.

Polyhydramnios

A condition where the amniotic fluid volume is more than expected for gestational age.

Amniotic fluid index (Polyhydramnios)

An ultrasound diagnostic criterion defined as $> 24\,cm$.

Deepest vertical pocket (Polyhydramnios)

An ultrasound diagnostic criterion defined as $\geq 8\,cm$.

Esophageal atresia

A fetal anomaly where the esophagus is not open, preventing fluid swallowing and leading to polyhydramnios.

Duodenal atresia

Obstruction of the duodenum that can cause polyhydramnios.

Fetal anemia

A condition that may lead to polyhydramnios, sometimes due to Rh incompatibility.

Diabetes mellitus

A maternal condition that is a common cause of polyhydramnios.

Rh incompatibility

A maternal condition where the mother's immune system attacks fetal blood cells, potentially causing polyhydramnios.

Umbilical cord prolapse

A potential complication of polyhydramnios.

Amnio-reduction

A treatment considered for severe forms of polyhydramnios.

Creatinine (Amniotic fluid)

Levels in amniotic fluid are similar to plasma levels.

Urea (Differentiation)

A better indicator than glucose or protein for distinguishing amniotic fluid from normal urine.

Protein (Amniotic fluid)

Present in the fluid at a concentration of $2\text{ to }8\,g/L$.

Glucose (Fluid differentiation)

Present in amniotic fluid but absent in normal urine.

Respiratory Distress Syndrome (RDS)

The most common cause of death in newborns, caused by insufficient surfactant production.

Surfactant

Substances produced in fetal lungs to decrease surface tension.

Fetal Lung Maturity (FLM) testing

Testing that assesses the viability of the fetus outside the uterus; of no value at $< 32\text{ weeks}$.

Lecithin

The major pulmonary surfactant required in fetal lungs.

Sphingomyelin

A phospholipid found in cell membranes produced at a constant rate after $33\text{ weeks}$.

L/S Ratio

The ratio of Lecithin to Sphingomyelin used to assess fetal lung maturity.

L/S parity timing

Lecithin and sphingomyelin are produced in equal amounts until $33\text{ weeks}$.

Mature L/S ratio

A result of $\geq 2.5$ suggests lung maturity.

Thin-layer chromatography

The technique used to determine the L/S ratio.

Blood contamination (L/S)

Decreases a mature L/S result and increases an immature L/S result.

Meconium contamination (L/S)

Makes L/S ratio results unreliable.

Phosphatidyl Glycerol (PG)

A lung surfactant not detectable until $35\text{ weeks}$ gestation.

Slide agglutination

A quick and simple technique to test for PG using anti-PG antibodies.

PG test advantage

The presence of blood or meconium does not affect the results.

Immature Interpretation (L/S & PG)

L/S ratio $< 2.0$ and PG is absent.

Indeterminate Interpretation (L/S & PG)

L/S ratio $\geq 2.5$ and PG is absent.

Mature Interpretation (L/S & PG)

L/S ratio $\geq 2.5$ and PG is trace or present.

Lamellar bodies

Storage granules for pulmonary surfactants present in the third trimester.

Lamellar body count

A value of $50,000\text{ to }200,000$ per microliter indicates maturity.

Automated hematology counter

A device (specifically the platelet counter) used to measure lamellar bodies.

Fetal erythroblastosis

Hemolytic disease of the fetus resulting from RBC hemolysis.

Bilirubin peak

An absorbance peak occurring at $450\,nm$ in scanned amniotic fluid.

$$\Delta A_{450}$$

The absorbance measurement used to correlate the amount of bilirubin with the severity of fetal hemolysis.

Oxyhemoglobin absorbance

Absorbs light at $412\text{ to }540\,nm$, making bloody specimens unacceptable for bilirubin testing.

Bilirubin scanning range

Absorbance is scanned from $365\text{ to }550\,nm$.

Liley Zone I

The zone on a semilog graph indicating a normal level of bilirubin.

Liley Zone II

The zone on a semilog graph indicating a marked level of bilirubin/severity.

Liley Zone III

The zone on a semilog graph indicating severe fetal hemolysis.

Semilog paper

Used to graph absorbance ($\Delta A_{450}$) against fetal age to determine severity zones.

Placenta

Helps produce amniotic fluid initially and is visualized during collection.

Fetal swallowing

A fetal activity that actively influences the composition of amniotic fluid later in pregnancy.

Fetal respiration

The movement of fluid into and out of fetal lungs that contributes to composition.

Fetal urination

The primary contributor to increased amniotic fluid volume late in pregnancy.

Probes and needles

Ultrasound probes and thin needles are tools used for amniocentesis collection.

Aseptic technique

The sterile method required for fluid collection to prevent infection.

Fetal epithelium

One of the cellular components found in amniotic fluid.

Amniotic membrane cells

Cells found in fluid derived from the amnion.

Inorganic salts

A component of the chemical composition of amniotic fluid.

Cascade approach

A recommended FLM testing strategy where tests are performed in series until a mature result is obtained.

Myotonic dystrophy

A CNS disorder that can be a cause of polyhydramnios.

Twin-to-twin transfusion syndrome

A condition in multiples that can lead to polyhydramnios.

Cystic lung malformations

A pulmonary anomaly that can cause polyhydramnios.

Fetal malposition

A potential complication resulting from polyhydramnios.

Urea (urine vs fluid)

High in urine and low in amniotic fluid, making it the best indicator for differentiation.

Lecithin production increase

Occurs rapidly at $34\text{ to }36\text{ weeks}$ of gestation.