Early Delivery: Neonatal Outcomes After Demonstrated Fetal Lung Maturity Before 39 Weeks of Gestation

Abstract & Commentary

By John C. Hobbins, MD, Professor, Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert.

Dr. Hobbins reports no financial relationship to this field of study.

Synopsis: Despite tests documenting fetal pulmonary maturity, delivering patients between 36 and 38 weeks gestation is associated with a greater chance of combined neonatal morbidity than if patients are delivered at 39-40 weeks without these tests.

Source: Bates E, et al. Neonatal outcomes after demonstrated fetal lung maturity before 39 weeks of gestation. Obstet Gynecol 2010;116:1288-1295.

The pendulum has been swinging away from doing early deliveries without indications, but the question remains: What is early? From this discussion emerges another question: Is it legitimate to justify delivering patients before, let's say, 39 weeks because there is amniotic fluid documentation of fetal pulmonary maturity?

A paper in the December 2010 issue of Obstetrics & Gynecology addresses these issues. The authors reviewed data from one center in Alabama from 1999 through 2008. They concentrated on patients who were between 36/0 and 38/6 weeks and were delivered after an L/S ratio (> 2) or a positive phosphatidyl glycerol (PG) suggested the fetuses were pulmonically mature (group 1). Outcomes of these infants were compared with those who were delivered without amniocentesis at 39 or 40 weeks (group 2). In both groups, gestational age was assessed using ACOG clinical guidelines. Exclusions were applied to both groups, which included fetal or maternal indications/complications that might skew the neonatal outcomes. The authors were interested in comparing various indicators of neonatal morbidity between the two groups.

In group 1 they found statistically increased risks for RDS (odds ratio [OR] = 7.6), need for "respiratory support" (OR = 2.0), surfactant use (OR = 6.5), hyperbilirubinemia requiring treatment (OR = 11.2), suspected or proven sepsis (OR = 1.7), NICU admissions (OR = 1.7), and hypoglycemia (OR = 5.8). The composite morbidity was two times higher for those delivered before 39 weeks, compared with those delivered after that time.

Commentary

This paper contains some important messages. Messing with Mother Nature can have unwanted consequences. Also, if infants are born between 36 and 38 weeks, a "positive" L/S ratio, PG, or, undoubtedly, fluorescent polarization does not afford complete immunity to common neonatal morbidities — including those involving the respiratory system. The L/S ratio and other indices of fetal lung maturity continue to be important tools in obstetrical management, especially in high-risk pregnancies. However, how old the fetus/infant is at the time of delivery seems to be more important than documentation of pulmonary maturity. Here the emphasis should be on early, precise dating of pregnancy, and amniocentesis, a procedure that is inconvenient, uncomfortable, expensive, and definitely not innocuous, should be reserved for clinical problems where there has been demonstrated benefit.