Fetal Lung Maturity: Optimal Testing Recommendations

Also known as: Fetal lung maturity (FLM) testing, assessed via Lecithin/Sphingomyelin ratio, Phosphatidylglycerol, Disaturated Lecithin, Lamellar Body Count, and Fluorescence Polarization

  • FLM testing is no longer recommended in any clinical scenarios involving pregnant women to aid in timing of delivery.
  • Demonstration of lung maturity with FLM is not sufficient to ensure maturity of other fetal organ systems.
  • If there is a clear medical indication for preterm or early-term delivery based on maternal and/or fetal conditions, delivery should occur regardless of lung maturity status.
  • There is no clinical utility for the individual tests.

Guidelines for Test Utilization

What does the test tell me?

In the past, FLM testing was used to determine whether the fetus' lungs were developed enough to allow for safe preterm or early-term delivery. In recent years, guidelines have shifted to state that there are other factors that should be used to determine whether to deliver a fetus, and FLM test results demonstrating mature lungs are not a rationale to proceed with delivery. These updated guidelines are based on several studies that have demonstrated worse outcomes with early-term births after FLM testing demonstrated lung maturity, relative to outcomes seen with full-term births.

Guidelines have also placed an emphasis on decreasing the rates of preterm and early-term births due to the well-established associated complications; therefore, demonstration of lung maturity should not be used to justify early delivery. [back to top]

When should I order this test?

FLM testing is no longer indicated to guide timing of preterm or early-term delivery. Providers should instead assess for maternal and/or neonatal conditions to determine whether there is an indication for early delivery. [back to top]

When should I NOT order this test?

Do not order this test for any clinical scenarios involving pregnant women. [back to top]

How should I interpret the result?

In the past, FLM testing results were reported as immature, borderline, or mature based on the levels of phospholipid measured. [back to top]

Is the test result diagnostic/confirmatory of the condition? If not, is there a diagnostic/confirmatory test?

No, studies have demonstrated that FLM testing alone is not sufficient to confirm adequate maturity of all organ systems to justify a preterm delivery. There are no other laboratory tests currently recommended to assess for fetal maturity. [back to top]

Are there factors that can affect the lab result?

The predictive value of FLM testing varies by gestational age. Blood and/or meconium stained amniotic fluid can impact certain FLM results. [back to top]

Are there considerations for special populations?

There are no special populations for which this test should be utilized. [back to top]

What other test(s) might be indicated?

Current guidelines recommend relying on other prenatal and maternal metrics, and not a laboratory test, to determine whether it is safe to proceed with a preterm or early-term delivery. [back to top]

References

ACOG Committee Opinion No. 765: Avoidance of Nonmedically Indicated Early-Term Deliveries and Associated Neonatal Morbidities. Obstetrics and Gynecology 133(2) (2019) e156-e163.

ACOG Committee Opinion No. 764: Medically Indicated Late-Preterm and Early-Term Deliveries. Obstetrics and Gynecology 133(2) (2019) e151-e155.


Last reviewed: March 2023. The content for Optimal Testing: the Association for Diagnostics & Laboratory Medicine’s (ADLM) Guide to Lab Test Utilization has been developed and approved by the Academy of Diagnostics & Laboratory Medicine and ADLM’s Science and Practice Core Committee.

As the fields of laboratory medicine and diagnostic testing continue to grow at an incredible rate, the knowledge and expertise of clinical laboratory professionals is essential to ensure that patients receive the highest quality and most useful laboratory tests. ADLM’s Academy and Science and Practice Core Committee have developed a test utilization resource focusing on commonly misused tests in hospitals and clinics. Improper test utilization can result in poor patient outcomes and waste in the healthcare system. This important resource geared toward medical professionals recommends better tests and diagnostic practices. Always consult your laboratory director to make sure these recommendations are appropriate for your patient population.