Fetal lung maturity

Question 1

What is the major type of phospholipid in surfactant?

Answer 1

Phosphatidylcholine (lecithin) - 80-85%

Phosphatidylglycerol - 10%

Question 2

What are the effects of antenatal steroids on RDS, IVH, BDP, and NEC?

Answer 2

RDS-in pooled metaanalysis, decreases by 50%, neonatal deaths, decreases by 50%, IVH-decreases, BDP-no effect, NEC-decreases

Question 3

Which of the following accelerates lung function? Corticosteroids, EGF-1, thyroxine

Answer 3

Thyroxine - no.
Corticosteroids - yes.
T3 is effective in stimulating surfactant synthesis in vitro and steroids combined with T3 produces an additive stimulation of surfactant production in vitro. T3 doesnäó»t cross the placenta but maternally administered TRH does.
TRH has shown increased TSH and T3 in umbilical cord blood. Absence of beneficial effects in human trials however.
Accelerate: steroids, TRH, T3, beta agonists, prolactin, EGF, TGF-alpha, estrogen, bombeisin.
Delay: adrogens, insulin, TGF-beta.

Question 4

What tests are commonly used to assess FLM?

Answer 4

The surfactant/albumin ratio (TDx-FLM ll), lecithin/sphingomyelin (L/S) ratio, lamellar body count, and detection of phosphatidylglycerol (PG) are the tests that have, in the past, been most commonly used to assess fetal lung maturity (table 1) [8]. The foam stability index and optical density at 650 nm are not widely used.

Question 5

What are the 2 types of tests used to detect FLM?

Answer 5

(1) biochemical tests measure the concentration of particular components of pulmonary surfactant
(2) biophysical tests evaluate the surface-active effects of these phospholipids.

Question 6

How do glucocorticoids induce pulmonary maturity?

Answer 6

Glucocorticoids act through reversible binding to the promoter region of genes that code for functional and structural proteins in various organs. In the lung, glucocorticoids induce lipogenic enzymes necessary for surfactant phospholipid synthesis and conversion of unsaturated to disaturated phosphatidylcholine, stimulate antioxidant surfactant protein (SP A-D) production and induce enzymes responsible for sodium and potassium channel ion and fluid flux.

Question 7

Risk of pulmonary hypoplasia w/ PPROM < 18w GA? <25w?

Answer 7

100% if < 18w, 50% if < 25w

Question 8

How does the proportion of lecithin and sphingomyelin change as pregnancy progresses?

Answer 8

Relative proportion of lecithin (disaturated phosphatidyl choline) and sphingomyelin are stable until the 32-33w, at which time the pulmonary active lecithin increases relative to the nonpulmonary sphingomyelin.

Question 9

What is the shake test for FLM?

Answer 9

Presence of stable foam ring 15 min after amniotic fluid is mixed with 95% ethanol. Correlates with L/S 1.5 or greater. Falsely immature results are common.

Question 10

What is the foam stability index for FLM?

Answer 10

The foam stability index (FSI) is a rapid predictor of fetal lung maturity based upon the ability of surfactant to generate stable foam in the presence of ethanol [34]. Ethanol is added to a sample of amniotic fluid to eliminate the effects of nonsurfactant factors on foam formation. The mixture is then shaken and will demonstrate generation of a stable ring of foam if surfactant is present. The foam stability index (FSI) is calculated by utilizing serial dilutions of ethanol to quantitate the amount of surfactant present. Blood or meconium interferes w/ results.

Question 11

What is TDx FLM?

Answer 11

Surfactant/Albumin ratio í¢ä‰åäóì S/A ratio (TDx FLM) Performed by evaluating competitive binding to surfactant and albumin by a ligand that exhibits fluorescence polarization (TDx FLM). Independent of fluid volume. A value of 50-70 mg/gm similarly predictive of PG and L/S. Blood or meconium in the amniotic fluid affects results.The manufacturer of the TDx-FLM II test has retired the analytical systems for TDx-FLM ll and ended production of the reagent required to perform it. Currently, there are no commercially available tests for measuring the surfactant/albumin ratio; however, new methods are in development

Question 12

How do lamellar bodies indicate +FLM?

Answer 12

Lamellar bodies are 1-5 micrometer diameter surfactant-containing particles secreted by type II pneumocytes. Increase with the onset of functional fetal pulmonary maturity. >50,000 is mature. < 15,000 is immature. Anything in between requires a second test. Can be contaminated by blood (because platelets are counted as lamellar body; the effect of meconium is minimal.)

Question 13

How is phosphatidylglycerol used in FLM testing?

Answer 13

Phosphatidylglycerol (PG) is a minor constituent of surfactant. It begins to increase appreciably in amniotic fluid after 35 weeks, several weeks after the rise in lecithin. Because PG enhances the spread of phospholipids on the alveoli, its presence indicates an advanced state of fetal lung development and function. Not affected by blood or meconium.

Question 14

How does optical density testing for FLM work?

Answer 14

An indirect measurement of lamellar bodies can be performed by measuring optical density of amniotic fluid at a wavelength of 650 nm. It is based upon the concept that increasing opalescence is due to increasing numbers of lamellar bodies. An optical density reading of í¢äóÁŒ«0.15 is used as the indicator of pulmonary maturity.

Question 15

How does meconium affect FLM testing?

Answer 15

Increases L/S by 0.1 to 0.2 in preterm and as much as 0.5 after 35 weeks
Recommend L/S 2.2/1 or 2.5/1 for meconium

Question 16

How does vaginal pool FLM test results correlate w/ amnio?

Answer 16

The FLM-TDx ll test (which is no longer available) on a vaginal pool specimen appeared to be reliable if a mature result is obtained.
By comparison, the lecithin/sphingomyelin ratio can be higher in the vaginal pool than in fluid from amniocentesis and false positive phosphatidylglycerol have been reported in vaginal pool samples due to bacterial contamination.

Question 17

How does blood contamination affect FLM testing?

Answer 17

Maternal serum has an intrinsic L/S of 1.3/1 to 1.5/1. Possibility blood could falsely elevate an immature result and lower a mature result. A mature result should thus be reassuring as an immature value could not be expected to increase to a mature level with blood contamination.PG is not affected by bloodTDx-FLM can be falsely lowered by blood, but a mature test reliably predicts fetal pulmonary maturity. Lamellar body count can be used in presence of blood with hematocrit <1%

Question 18

How does diabetes affect FLM testing?

Answer 18

1. Hyperinsulinemia and hyperglycemia decrease incorporation of choline into phosphatidylcholine and decreases PG production
2. Hyperinsulinemia prevents cortical induced phosphatidylcholine and disaturated phosphatidylcholine production by type II pneumocytes and appears to cause a delay in morphologic pulmonary maturation
3. Increased risk of RDS despite mature L/S could be due to increase myoinositol with hyperglycemia. Enhances phosphatidyl inositol to detriment of PG. However, the current consensus is that the same threshold value for lung maturity can be used for both nondiabetic and diabetic patients (pregestational or gestational diabetes).

Question 19

Which FLM tests are reliable despite oligo- or polyhydramnios?

Answer 19

The effect of amniotic fluid volume (oligohydramnios, polyhydramnios) on test results has not been studied extensively. Theoretically, tests that are expressed as a ratio or proportion of two solutes released into the amniotic fluid should remain accurate independent of amniotic fluid volume, while tests that reflect the concentration of a substance in the amniotic fluid (eg, lamellar body count, phosphatidylglycerol) may be affected by amniotic fluid volume.

Question 20

Which FLM tests are reliable in the presence of blood or meconium?

Answer 20

PG, S/A ratio