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Assessment of fetal lung maturity

Jonathan Gillen-Goldstein, MD
Andrew P MacKenzie, MD
Edmund F Funai, MD
Section Editor
Charles J Lockwood, MD, MHCM
Deputy Editor
Vanessa A Barss, MD, FACOG


The pulmonary system is among the last of the fetal organ systems to mature, both functionally and structurally. Fetal sex and race/ethnicity appear to play a role in this process; respiratory problems near term are more common among white male fetuses than among female fetuses, blacks, and South Asians [1,2].

Because the immature pulmonary system may not oxygenate the neonate adequately, preterm birth can lead to significant neonatal morbidity or mortality. Therefore, fetal lung maturity is sometimes assessed before iatrogenic preterm delivery and can be a factor in determining the timing of delivery in these cases. Several laboratory tests are available for this purpose. All involve testing amniotic fluid and provide an indirect assessment of the likelihood of lung maturity; direct studies of fetal lung function are not possible.

This topic will discuss tests for assessment of fetal lung maturity. Clinical manifestations, diagnosis, treatment, sequelae, and prevention of neonatal pulmonary immaturity are reviewed separately. (See "Pathophysiology, clinical manifestations, and diagnosis of respiratory distress syndrome in the newborn" and "Prevention and treatment of respiratory distress syndrome in preterm infants" and "Antenatal corticosteroid therapy for reduction of neonatal respiratory morbidity and mortality from preterm delivery".)


In most clinical settings, testing for fetal lung maturity is not performed because (1) delaying delivery because of lung immaturity would place the mother or fetus at significant risk, or (2) the fetus would benefit from delaying delivery, even if lung maturity is documented, and delaying delivery does not place the mother at significant risk [3]. However, these assessments are not always black and white, and information about lung maturity may sometimes be helpful in the balance [4]. Also, the information may be helpful in estimating the level of newborn care that will be required. Thus, a test for fetal lung maturity may be performed before semielective but medically indicated births <39 weeks when this information significantly impacts assessment of the balance between the maternal-fetal risks of continuing the pregnancy versus the maternal-fetal risks of preterm birth. This is an infrequent occurrence.

Tests for fetal lung maturity are generally not performed before 32 weeks of gestation, given the high prevalence of fetal pulmonary immaturity and the lower predictive value of a mature test result at this gestational age.


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Literature review current through: May 2017. | This topic last updated: Jun 01, 2017.
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