hello my name is David Grenache I'm an
associate professor of pathology at the
University of Utah and a medical
director at ARUP laboratories the
development of the human lung is an
exquisitely regulated and highly
coordinated process of branching
morphogenesis angiogenesis and alveolar
ization a critical event in lung
development is the synthesis of
pulmonary surfactant that begins during
the third trimester of pregnancy and
prepares the lung to function as a gas
exchange organ after delivery
pulmonary surfactants function to
decrease surface tension inside lung
alveoli which prevents the collapse of
alveoli upon exhalation infants that are
born prematurely are at risk of
developing respiratory distress syndrome
or RDS due to a deficiency of pulmonary
surfactant it is well known that the
incidence of RDS decreases with
increasing gestational age of delivery
such that the risk of RDS is very high
in preterm infants and low in those born
at term fortunately there are effective
treatments for RDS the administration of
corticosteroids to a woman with
threatened preterm delivery can increase
the production of fetal surfactant and
thereby decrease the risk of RDS if the
infant is delivered preterm for infants
who do develop RDS the administration of
exogenous surfactant is a very effective
intervention in 2010 RDS was the eighth
leading cause of infant death in the
United States and so the prevention and
treatment of RDS continues to be an
issue of critical importance in newborn
medicine clinical tests are available
that assess the maturity of fetal lungs
these tests are performed on amniotic
fluid and determine if a sufficient
amount of pulmonary surfactant is
present to prevent the development of
RDS between 1971 in 1988 several fetal
lung maturity tests or FLM tests were
developed but only three are
presently in clinical use these include
the lecithin to sphingomyelin ratio the
detection of phosphatidyl glycerol and
the lamellar body count these FLM tests
exhibit high sensitivity for immaturity
and an excellent mature predictive value
however because there are many false
immature results the specificity is poor
as is the predictive value of an
immature result so while a mature result
is a very strong indicator of pulmonary
maturity an immature result is not a
good predictor of RDS despite the
excellent performance of fetal lung
maturity tests there has been a recent
decline in their utilization published
surveys have reported declining rates of
flm tests ordered by physicians and when
asked why their belief that these tests
are no longer needed for patient care is
cited as the major reason for the
decline this decrease in flm test
utilization is reflected in their annual
testing volumes that we have observed at
ARUP while FLM test orders remained
rather steady between 2007 and 2011 a
rapid decline was noted in 2012 that was
sustained to the present day most
importantly there are several lines of
evidence to support a decrease in fetal
lung maturity test utilization in its
2008 practice bulletin on fetal lung
maturity testing the American College of
Obstetricians and Gynaecologists
recommended that FLM testing only be
performed to demonstrate pulmonary
maturity before a scheduled to delivery
at less than 39 weeks of gestation
however the same group strongly
discourages the practice of scheduled
delivery before 39 weeks of gestation
unless it is justified by medical or
obstetric complications in agreement
with these guidelines several studies
have demonstrated that the delivery of
infants before 39 weeks of gestation
even with a mature fetal lung maturity
test result is associated with an
increased risk of neonatal respiratory
complications including RDS transient
tachypnea of the new
born pneumonia and respiratory failure
one multicenter study that examined
neonatal outcomes of infants born
between 36 and 38 weeks that had mature
fetal lung maturity test results
reported that the incidence of adverse
outcomes in that population was 2.5
times greater compared to neonates born
between 39 and 40 weeks another study
also reported a significantly greater
risk of adverse outcomes for neonates
born between 37 and 38 weeks with mature
fetal lung test 2 those born after 39
weeks prompting the authors to conclude
that one documented fetal lung maturity
testing is insufficient to determine an
infant's readiness for postnatal life 2
that fetal lung maturity testing is
irrelevant when preterm delivery is
medically necessary and 3 that infants
should not be delivered electively prior
to 39 weeks of gestation
even if lung maturity is demonstrated in
light of this it is time to consider if
fetal lung maturity tests are medically
necessary given that there are effective
therapies for infants at risk for or who
develop RDS that elective delivery
before 39 weeks of gestation is strongly
discouraged and that the assessment of
fetal lung maturity is irrelevant if
preterm delivery is medically necessary
in summary currently available fetal
lung maturity tests have high
sensitivity for identifying pulmonary
immaturity and have high predictive
values for lung maturity still the
frequency of fetal lung maturity testing
is declining likely because they do not
improve a fetal outcome as is evidenced
by studies that have shown that fetal
lung maturity testing is not associated
with a lower risk of adverse neonatal
outcomes add to that the fact that
advances in neonatal care such as
antenatal corticosteroid therapy and surfactant
replacement therapy have significantly
decreased infant mortality rates due to
RDS it is logical to conclude that fetal
lung maturity testing in modern
obstetric medicine has come to the end
of its era of
usefulness
