- Can we reduce the rate of scheduled births that occur earlier than 39 weeks of gestation? Examining the Evidence.
Commentary by George A. Macones, MD, MSCE
(OBG Management, June 2010)
AUGUST 2010—An analysis of more than 200,000 deliveries finds that babies born between 34 weeks and 37 weeks are more likely to have severe respiratory illness than those born at term, and that this risk decreases with each added week of gestational age during the late preterm period. The report of the study was published in the July 28 issue of JAMA.
Late preterm birth (34 0/7 to 36 6/7 weeks’ gestation) accounts for 9.1% of all deliveries and 75% of all preterm births in the United States. Considerable evidence has shown that short-term illnesses are prevalent; however, much of the supporting data for that evidence is more than a decade old or drawn from small populations, according to background information in the article.
Judith U. Hibbard, MD, of the University of Illinois at Chicago, and colleagues of the National Institutes of Health’s Consortium on Safe Labor, conducted a study to determine the rate of respiratory illness among late preterm births by analyzing recent data from a large group of late preterm infants. The study included electronic data from 12 institutions (19 hospitals) across the United States on 233,844 deliveries between 2002 and 2008. Charts were abstracted for all newborns with respiratory problems admitted to a neonatal intensive care unit (NICU), and late preterm births were compared with term births in regard to resuscitation, respiratory support, and respiratory diagnoses.
Of 19,334 late preterm births, 7,055 (36.5%) were admitted to a NICU and 2,032 had respiratory compromise. Of 165,993 term infants, 11,980 (7.2%) were admitted to a NICU, 1,874 with respiratory illness. The researchers found that respiratory distress syndrome (RDS) was the most common respiratory illness, occurring in 10.5% (n = 390) of 34-week deliveries, decreasing with gestational age to 0.3% (n = 140/41,764) at 38 weeks. Transient tachypnea of the newborn was the second most common morbidity at 6.4% (n = 236) at 34 weeks, reaching a low of 0.3% (n = 207/ 62,295) at 39 weeks. Also decreasing from 34 weeks were pneumonia, from 1.5% to 0.1% at 39 weeks, and overall respiratory failure, from 1.6% to 0.09% at 40 weeks. The percentage of infants who had respiratory illness decreased significantly as gestational age increased until 39 to 40 weeks.
Additional analysis found that newborns born at 34 weeks had a 40-fold increase in the odds of RDS; that risk decreased with each advancing week of gestation until 38 weeks.
“Even at 37 weeks, the odds of RDS were still 3-fold greater than that of a 39- or 40-week birth. Similar patterns were seen for transient tachypnea of the newborn, pneumonia, standard or high-frequency ventilator requirements, and respiratory failure,” according to the authors of the report.
“We suggest that future studies should focus on indications for late preterm birth. Only by more completely understanding reasons for rising rates of late preterm birth might clinicians be able to initiate salutary interventions to decrease neonatal respiratory morbidity. Improved pregnancy dating through early ultrasound confirmation of estimated due date may help prevent neonatal morbidity associated with erroneous delivery of a neonate that is actually at an earlier gestational age. Finally, a better understanding of the effect of mode of delivery on neonates may help with future interventions to decrease morbidity.”
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