Amniotic fluid analysis

Chapter 14

what are three reasons why we would evaluate amniotic fluid?

• diagnose genetic and congential disorders early in gestation ( 15-18 weeks)

• assess fetal pulmonary maturity (32-42 weeks)

• estimate and monitor degree of featl anemia caused by isoimmunization or infection

what is the amnion?

a membrane composed of a single layer of cubodial epithelial cells between the placenta and the amniotic cavity

what is the purpose of the amniotic fluid?

-protects the fetus

- enabling movement

-biochemical processes (nutrient rich for the baby)

what initially, is amniotic fluid made out of ?( before baby plays a role in composition)

distylate of plasma

What role does the baby play in the compostion of amniotic fluid ?

water and solutes are exhanged between the fetus and the surrounding fluid via swallowing, respiration, and urination

why can we evaluate fetal lungs by looking at the amniotic fluid?

the fetus’s lungs produce fetal lung surfactants, which they “breathe out” into the fluid surrounding them

as the baby ingests water and electrolytes, the fetus uses that for metabolic processes, they byproducts, such as urea, creatinine, and uric acid are removed by the baby through urination, the mom’s blood comes and picks up the babysitter waste products, and delivers more water and electrolytes

;)

at 12 weeks of pregnancy, what it the volume of the amniotic fluid?

25-50 mL

at 37 weeks of pregnancy, what is the volume of the amniotic fluid?

800-1200 mL

volume of anmiotic fluid increases through pregnancy from 25 to 50 mL at “—” weeks to 800 to 1200 mL at “—” weeks

12 weeks, 37 weeks

what kind of contianer is necessary for amniotic fluid collection?

PLASTIC!!! cells adhere to glass container walls!

how much amniotic fluid does the physician aspirate off?

10-20 mLw

should amniotic fluid have blood in it?

no, unless traumatic tap

why do we cover amniotic fluid samples with aluminim foil?

to prevent light exposure and the photo-oxidation of bilirubin ( an indicator of HDFN)

Is this sample amniotic fluid or urine? This sample is amniotic fluid because…

glucose, protein and creatinine similar to plasma is present ( urine should have no glucose or protein and have high cretinine and high urea)

yellow or amber amniotic fluid

bilirubin

green amniotic fluid

meconium from fetal intestineem

meconium

gelatinous or mucus like material that forms in the fetal intestines as a result of swallowed amniotic fluid and fetal intestinal secretions

in terms of clarity, all amniotic fluid is somewhat “—”

turbid

is it in early or late pregnancy where there is little particulate matter?

early … fluid is not very turbid

is it in early or late pregnancy where there is little particulate matter?

late… more turbid due to increased fetal cells, hair, and vernix in fluid

what is one of the last organs to mature in a fetus?

lungs

Why would we need to ascess fetal lung maturity?

we need to ensure that if necessary for a premature delivery (due to fetal stress) that the baby will be able tho breathe on its own

up untill what week will the fetal lungs start to develop?

32 weeks

why is there no value in testing fetal lung maturity at less than 32 weeks?

all tests will indicate immaturity at that stage, becuase the lung development isnt there yet

what is the most common cause of death in newborns?

respiratory distress syndrome (RDS)

what does respiratry distress syndrome result from?

insufficent productuion of surfactant the alveolar surfaces in the newbrons lungs

normally, epithelial cells in the lungs produce and secrte phospholipids and proteins in the form of “—-” these release surfactant into the alveolar air space

lamellar bodies

what happens physiologically when a baby has no surfactant?

they can breathe in their first breathe, but after their first breath the alveoli collapse and completely close, the baby has to work super hard just to reinflate the lungs… leads to exhaustion, hypoxia, and respiratory acidosis

fetal lung maturity was sound to be related to specific “—” in the amniotic fluid

phospholipids

the probability of RDS relies on what two factors?

results of FLM test and gestational age of fetus at time of testing

“—” is the major pulmonary surfactant that prevents alveolar collapse by decreasing surface tension and allows gas exchange

lecithin

water lines the alveolus and water wants to stick together . they constantly want to pull the alveoli inward to be next to eachother. If this happened, the alveoil would collapse in on itself BUT surfactant prevents them from pulling so stronly to another

:)

what is the other phospholipid besides lecithin that is a part of the surfactant ?

sphingomyelin

usually spingomyelin and lectincin are in equal amounts up untill 33 weeks, but at 34-36 weeks ,”—-” increases while “—-” stays constant

lecithin increases while sphingomyelin stays constant

an L/S ratio greater than or equal to “—” indicates maturity of fetal lungs where less tahn that indicates immaturity

2.0

how does the presence of blood affect a mature L/S ratio result

makes it seem more immature

how does the presence of blood affect a mature L/S ratio result?

makes more immature

how does the presence of blood affect a immature L/S ratio result?

makes it seem more mature

the L/S ratio test is a better predictor of maturity or immaturity?

maturity

what surfactant phospholipid is not detectable until 35 weeks gestation?

Phosphatidyl Glycerol

what is the principle of the PG test?

polyclonal anti-PG agglutinates lamellar bodies that contain phosphatidyl glycerol so we can observe visible agglutination

what is a disadvantage of the PG test?

lots of false negatives ( negative results don’t add anything)

can’t be used until late pregnancy

what is an advantage of the PG test?

very specific ( a positive result is clinically valuable)

are PG tests affected by blood or meconium?

nope!

shake test aka…

foam instability index

if there is adequate surfactant in amniotic fluid a foam can be produced by surfactancts when shaken with different dilutions of “—”

ethanol

FSI of greater than or equal to 0.47 is maturiy or immaturity?

maturity

where are pulmonary surfactants stored?

lamellar bodies

secretion of lamellar bodies into the fetus’s alveolar lumen begins at 20-24 weeks gestation, but when does it become present in the amniotic fluid?

third trimester

in the thrid trimester, what quantites can we see lamellar bodies in the amniotic fluid?

50,000-200,000 per microliter

What level of Lamellar bodies in the amniotic fluid signals that the fetus has reached lung maturity?

greater than 50,000

what are the advantages of lamellar body counts?

rapid, low cost, and samll sample size

why can’t we use bloody specimeans for lamellar-body counts?

platelets cause interferencehs

is it normal to see bilirubin in amniotic fluid?

no

the amount of bilirubin correlates with serverity of “—”

hemolysis

where does bilirubin casue a peak on the normal striaght line amniotic fluid ( 365-550)

450 nm

how does oxyhemoglobin interfere with the absorbance of what would be normal, straight line amniotic fluid?

410 and 540

what is the Queenan chart used for?

used to evaluate severity of hemolysis between 14 and 40 weeks gestation… divided into 4 zones