Lecture 9 Amniotic Fluid Analysis

Amniotic fluid is contained within a membrane called the amnion.

The primary function of amniotic fluid is to protect the fetus.

Amniotic fluid is initially produced by the amnion and placenta.

Later in pregnancy, the fetus contributes to the composition of amniotic fluid through swallowing, respiration, and urination.

The volume of amniotic fluid increases from 25 to 50 mL at 12 weeks to between 800 to 1200 mL at 37 weeks.

Oligohydramnios, which can result from rupture of the amniotic fluid, and polyhydramnios, which can occur if the fetus drinks less amniotic fluid.

single layer of cuboidal epithelial cells (inner surface)

water (around 98%), with the remaining 2% made up of electrolytes, nutrients, hormones, antibodies, proteins, and other substances like fetal cells

a prenatal procedure that involves extracting a small amount of amniotic fluid from the womb using the aseptic technique with long sterile needle to check for fetal health conditions

transabdominally or vaginally with simultaneous ultrasound exam

diagnosis of genetic and congenital disorders
assessment of fetal lung maturity
estimate and monitor degree of fetal distress.

Early diagnosis allows for the detection of conditions such as neural tube defects, which can cause severe damage to the spinal cord and brain.

Diagnosis is typically conducted between 15 to 18 weeks of gestation, usually after 14 weeks.

This assessment is done later because the lungs are the last organ to mature in the fetus.

Fetal lung maturity is assessed between 32 to 42 weeks of gestation.

Conditions that may require monitoring for fetal distress include preeclampsia, maternal diabetes mellitus, Rh factor incompatibility, cystic fibrosis, sickle cell disease, older maternal age, infection, and anemia.

10-20 mL of fluid colllected by physician into numbered syringes

plastic containers and protected from light!! (covered in aluminum foild or ambered color container because biliruben is sensitive to light!!)

because cells can adhere to glass

light and time and temperature are sensitive

high speed

low speed to not damage cells.

amniotic fluid contains:
glucose
protein 2-8 g/L
creatinine similar to plasma

normal urine
no glucose
no protein
high creatinine
high urea

urea because diabetes or kidney disease can cause abnormal readings compared to nromal urine

colorless or pale yellow

Early pregnancy: not much particulate matter
Late pregnancy: more turbid; increased fetal cells, hair, and vernix (grease from baby's skin) in fluid

high speed or filtration

Karyotyping and genetic counseling

used to assess viability of fetus outside uterus

From insufficient production of surfactant in newborn's lungs :(

inside alveoli

Type 2 cells (cubodial epithelial cells)

to prevent lung collapse

responsible for gas exchange.

Respiratory Distress Syndrome (RDS) is a condition often related to fetal lung immaturity, characterized by difficulty in breathing after birth due to underdeveloped lungs.

The probability of RDS is determined by two factors:
1. the results of fetal lung maturity (FLM) tests and
2. the gestational age of the fetus at the time of testing.

This indicates the maturity of the fetus's lungs.

The recommended approach is a cascade approach, where a series of fetal lung maturity (FLM) tests are performed until a mature result is obtained or all tests have been completed.

Gestational age is important because it helps assess the developmental stage of the fetus, which can affect the likelihood of the lungs being mature enough to avoid RDS.

A cascade approach in FLM testing involves performing multiple tests in sequence to evaluate lung maturity until a mature result is found, indicating that the lungs are sufficiently developed.

one of the tests for fetal lung maturity

Phospholipids are required in fetal lungs to decrease surface tension. They act as surfactants, which are essential for lung function and help prevent lung collapse.

Lecithin is a major pulmonary surfactant in the lungs that helps reduce surface tension, enabling proper lung expansion and function.

Sphingomyelin is a phospholipid found in cell membranes. In the context of fetal lung maturity, it is used as a reference point for lecithin levels in the L/S Ratio.

Lecithin levels begin to increase significantly at around 34 to 36 weeks of gestation, while sphingomyelin levels either remain constant or decrease.

An L/S Ratio of 2.5 or greater is considered indicative of fetal lung maturity, suggesting that the lungs are likely mature enough to function well after birth.

Until about 33 weeks of gestation, lecithin and sphingomyelin are produced in approximately equal amounts.

thin-layer Chromatography technique is commonly used to measure the levels of lecithin and sphingomyelin in amniotic fluid for calculating the L/S Ratio.

presence of blood in specimen decreases a mature result and increases an immature result!

Meconium-contaminated specimens

MATURITY.

Phosphatidyl glycerol (PG)

at 34 weeks and on. not detectable until 34 week gestation.

Thin-layer chromatography or slide agglutination using anti-PG antibodies.

Total lung capacity (TLC)

NO

blood or meconium (fetal poop)

postive tests are most likely indicate the presence of PG
DOWN SIDE IS THERE ARE MANY FALSE-NEGATIVES, meaning they often fail to detect PG when it is actually present.

L/S ratio > or = 2.5 AND "trace" of phosphatidylglycerol

a diagnostic test used to assess fetal lung maturity.

L/S ratio; Phosphatidyl glycerol (PG); Lamellar Body Counts

are small storage granules within type 2 cells that contain surfactant. These bodies are produced by the fetal lungs and eventually released into the amniotic fluid, where they can be counted.

3rd trimester; 50,000 to 200,000 per microliter

Automated hematology counter's platelet counter because its at rapid, low-cost, small sample size needed.

yes!!

Rh factor incompatibility between mother and fetus

Rh- mother
Rh+ fetus

The mother’s immune system may respond by producing antibodies against the Rh-positive cells, a process known as sensitization. This doesn’t typically affect the first pregnancy, as sensitization usually takes time. In a later pregnancy with another Rh-positive fetus, the mother's anti-Rh antibodies can cross the placenta and attack the fetus’s Rh-positive red blood cells. This can lead to hemolytic disease of the fetus and newborn (HDFN)

Rh incompatibility is managed by giving Rh-negative mothers an injection of Rh immunoglobulin (RhIg or RhoGAM) during and after each pregnancy.

not in normal condition, only is significant fetal red blood cell hemolysis occurs.

severity of hemolysis

365 to 550 nm

450 nm

bloody specimens because oxyhemoglobin aborbs at 412 to 540 nm
&
meconium -contaminated specimen also not acceptable.
REJECT SAMPLE

must be protected from light after collection, as bilirubin is very light sensitive.