Fewer infants are being delivered early, and there has been a decline in neonatal mortality, according to a retrospective cohort study of more than 34 million singleton live births.
Researchers presented the results of a study in the May 14 online edition of JAMA Pediatrics that attempted to quantify changes in gestational age distribution and gestational age–specific perinatal mortality in the United States between 2007 and 2015.
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However the proportion of births at a gestational age of 39-40 weeks increased from 54.5% to 60.2% in that same time period.
“The decreasing proportion of births at gestational ages of 34-36 and 37-38 weeks may be associated with changes in the timing of elective delivery, with hospital policies and quality initiatives effectively reducing unindicated deliveries before 39 completed weeks of gestation,” wrote Cande V. Ananth, PhD, of Columbia University, New York, and coauthors.
“Increased use of low-dose aspirin in women with ischemic placental disease may additionally have resulted in decreased need for indicated delivery before 39 weeks.”
At the same time, perinatal mortality rates decreased overall, from 9 per 1,000 births in 2007 to 8.6 per 1,000 births in 2015, but increased significantly in gestational ages 32-33 weeks (7%), 34-36 weeks (15%), and 37-38 weeks (23%) over that period. There was also a significant 31% increase in perinatal mortality at gestational age 42-44 weeks, but decreases at 20-27 weeks and 39-40 weeks.