Fetal lung maturity tests. Are they truly necessary?

When infants are born before 39 completed weeks of gestation, they are at increased risk of developing respiratory distress syndrome (RDS).  The risk of RDS increases as the gestational age of the infant at delivery decreases.  In other words, the more premature a baby is born, the more likely it is that it will have RDS.

This is a primary reason why an elective delivery before 39 weeks of gestation should not take place unless the fetal lungs are shown to be mature using fetal lung maturity tests.  The logic behind that mandate should be obvious: infants that develop RDS can die and those that do survive often develop other serious complications like septicemia,  necrotizing enterocolitis, retinopathy, and developmental handicaps.

Intuitively, it makes sense that if lab testing demonstrates mature fetal lungs then the risk of RDS, and its associated complications, would be low and elective delivery before 39 weeks could be permitted.  However, a recent study showed that even after documented fetal lung maturity, infants born before 39 weeks were at higher risk of adverse outcomes than infants born at 39 to 40 weeks.

Infants born before 39 weeks were, overall, at 1.6-fold greater risk of having something bad happen to them.  Things like elevated serum bilirubin, ventilator support, low blood glucose, admission to a neonatal intensive care unit, or even RDS!

Results like these definitely call into question the current convention that delivery before 39 weeks is okay if fetal lung maturity is confirmed by lab testing.  One has to even wonder why fetal lung maturity tests are even necessary.  Perhaps they aren't.

Due to improvements in gestational age dating, maternal administration of corticosteroids that accelerate fetal lung maturity in at-risk pregnancies, and exogenous surfactant replacement therapies, the number of newborn deaths due to RDS has declined considerably over the last 15 years.  Also, doctors are ordering fewer fetal lung maturity tests than they have in the past.  They probably aren't going to go away any time soon but all signs are pointing towards their demise.

A growing body of evidence is telling us that 1) elective delivery of infants before 39 weeks of gestation should be avoided; 2) that's true even if their lungs are shown to be mature by lab testing; and 3) testing for fetal lung maturity is decreasing.

Perhaps it is time to send these tests away once and for all.

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