Fetal Lung Maturity

Clinical Background

Prematurity is associated with numerous complications, including neonatal respiratory distress syndrome (RDS) and low birth weight; both are major causes of infant morbidity and mortality.

Epidemiology

Risk of RDS is inversely related to gestational age at birth
- >60% at <30 weeks of age
- 20% at 34 weeks of age
- <5% at >36 weeks of age

Pathophysiology

Pulmonary surfactants are synthesized by type II pneumocytes, packaged into storage granules called lamellar bodies, and function to decrease alveolar surface tension
RDS is caused by deficiency of pulmonary surfactant leading to alveoli collapse, hypoxia, hypercapnia and acidosis

Tests

Tests generally appear in the order most useful for common clinical situations

Test name: Fluorescence Polarization (Fetal Lung Maturity)

ARUP #: 0020486

Methodology: Fluorescence Polarization

Use:

Assess fetal lung maturity (FLM) to time delivery of fetus for optimal outcome

Assess need for intratracheal administration of exogenous surfactant in premature births

Test of choice for urgent clinical situations

Limitations:

Blood contamination can change results, but immature result will not be classified erroneously as mature

Evaluate reports of FLM with caution, since no gold standard exists

Follow-up:

For immature results, consider another FLM test (cascade testing)

Test name: Lamellar Body Counts

ARUP #: 0080940

Methodology: Automated Cell Count

Use:

Use in obstetric situations involving premature labor, premature rupture of membranes, management of eclampsia fetal distress and elective delivery at term

Test requires less than 10 minutes to determine FLM

Limitations:

Do not apply the reference values for test to other instruments without performing comparison studies

Do not use vaginal pool specimens or specimens with >0.5% blood as presence of platelets will artificially inflate count of lamellar bodies

Do not use frozen samples

Follow-up:

For immature results, consider another FLM test (cascade testing)

Test name: Lecithin-Sphingomyelin Ratio

ARUP #: 0080200

Methodology: Chromatography

Use:

Traditional test for predicting fetal lung maturity

Requires a minimum of 4 hours for results

Test of choice for rapid screening is fluorescence polarization

Limitations:

Blood contamination (>0.5%) introduces plasma lipids, which increases low values and decreases high values

L/S ratio is slower and less precise than fluorescence polarization

Follow-up:

Test name: Phosphatidylglycerol

ARUP #: 0080275

Methodology: Immune Agglutination

Use:

Often ordered for assessment of FLM when mother has diabetes

Positive result indicates maturity

Negative result unhelpful

Limitations:

No modern studies exist that show that PG needed for diabetic patients

10% of healthy term infants have no measurable PG

Follow-up:

For immature results, consider another FLM test (cascade testing)

Additional Tests Available

Test name: Fetal Fibronectin

ARUP #: 0082024

Methodology: Semi-Quantitative Solid Phase/Immunosorbent

Comments:

References

General References

Ashwood ER. Markers of Fetal Lung Maturity. In Gronowski AM, ed. Handbook of Clinical Laboratory Testing During Pregnancy. Totowa, NJ: Humana Press, 2004. pp. 55-70.

Grenache DG, Gronowski AM. Fetal lung maturity. Clin Biochem. 2006;39(1):1-10.

Gronowski AM, Parvin CA. Prediction of risk for respiratory distress syndrome using gestational age and the TDx-FLM II assay. Am J Obstet Gynecol. 2003;189(5):1511-1512.

Haymond S, Luzzi VI, Parvin CA, Gronowski AM. A direct comparison between lamellar body counts and fluorescent polarization methods for predicting respiratory distress syndrome. Am J Clin Pathol. 2006;126(6):894-899.

Kesselman EJ, Figueroa R, Garry D, Maulik D. The usefulness of the TDx/TDxFLx fetal lung maturity II assay in the initial evaluation of fetal lung maturity. Am J Obstet Gynecol. 2003;188(5):1220-1222.

Neerhof MG, Dohnal JC, Ashwood ER, Lee IS, Anceschi MM. Lamellar body counts: a consensus on protocol. Obstet Gynecol. 2001;97(2):318-320.

Parvin CA, Kaplan LA, Chapman JF, McManamon TG, Gronowski AM. Predicting respiratory distress syndrome using gestational age and fetal lung maturity by fluorescent polarization. Am J Obstet Gynecol. 2005;192(1):199-207.

Szallasi A, Gronowski AM, Eby CS. Lamellar body count in amniotic fluid: a comparative study of four different hematology analyzers. Clin Chem. 2003;49(6 Pt 1):994-997.

Tanasijevic M. Predictive model for fetal lung maturity assessment incorporating Abbott FLM S/A II test results and obstetric estimates of gestational age. Clin Chim Acta. 2002;326(1-2):1-2.

Ventolini G, Neiger R, Hood D, Belcastro C. Update on assessment of fetal lung maturity. J Obstet Gynaecol. 2005;25(6):535-538.

Wijnberger LD, Huisjes AJ, Voorbij HA, Franx A, Bruinse HW, Mol BW. The accuracy of lamellar body count and lecithin/sphingomyelin ratio in the prediction of neonatal respiratory distress syndrome: a meta-analysis. BJOG. 2001;108(6):583-588.

ACOG educational bulletin. Assessment of fetal lung maturity. Number 230, November 1996. Committee on Educational Bulletins of the American College of Obstetricians and Gynecologists. Int J Gynaecol Obstet. 1997;56(2):191-198.

References from the ARUP Institute for Clinical and Experimental Pathology Research®

Chapman JF, Ashwood ER, Feld R, Wu AH. Evaluation of two-dimensional cytometric lamellar body counts on the ADVIA 120 hematology system for estimation of fetal lung maturation. Clin Chim Acta. 2004;340(1-2):85-92.

Medical Reviewers

Grenache, David G., Ph.D. Medical Director, Special Chemistry at ARUP Laboratories; Assistant Professor, Clinical Pathology, University of Utah

Meikle, A. Wayne, M.D. Medical Director, RIA and Endocrinology at ARUP Laboratories; Professor of Internal Medicine and Pathology, University of Utah

Comprehensive Review: November 2007
Last Update: March 2008