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Increasing number of infants carried to term in the US
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In the United States, singleton births at 30 and 40 weeks’ gestational age increased to 60.2% of all births in 2015, with a decrease in perinatal mortality observed for neonates born at these ages, according to research published in JAMA Pediatrics.
“Preterm delivery rates among live births have decreased in the U.S. from 2005 to 2014 and in several European countries,” Cande V. Ananth, PhD, MPH, from the department of obstetrics and gynecology in the College of Physicians and Surgeons and the department of health policy and management at the Joseph L Mailman School of Public Health, Columbia University, and colleagues wrote “However, the rates began increasing in 2015 and 2016 in the U.S. Because reductions in preterm and early term deliveries and perinatal mortality remain a global health priority, determining the association between gestational age distribution and perinatal mortality remains a challenge.”
To determine the changes that have occurred in perinatal mortality by gestational age, with specific focus on gestational age distribution, the researchers conducted a retrospective cohort study in which they assessed linked birth data on live births and infant deaths. All infants were singleton births and born between 2007 and 2015.
Age groups were split into 20 to 27 weeks’, 28 to 31 weeks’, 34 to 36 weeks’, 37 to 38 weeks’, 39 to 40 weeks’, 41 weeks’, and 42 to 44 weeks’ gestational age. The changes in number of births and perinatal mortality were analyzed, with mortality defined as stillbirth at 20 weeks’ gestational age or older and neonatal death at 27 days or younger. Furthermore, Ananth and colleagues examined how the age of the infant contributed to changes in mortality rates. The trends in neonatal mortality were calculated using log-linear regression models that were adjusted for confounders.
Of the 34,336,577 births included in the study, the number of live births decreased between 2007 and 2015; however, an increase was observed for infants born at 39 to 40 weeks’ gestational age within this study period (54.5% to 60.2%).
Trends demonstrated a decrease in the rate of perinatal mortality (9.0 to 8.6 per 1,000 births). Additionally, decreases also were observed in the rates of stillbirth (5.7 to 5.6 per 1,000 births) and neonatal mortality (3.3 to 3.0 per 1,000 births).
Although the proportion of births decreased for several age cohorts, the researchers observed annual adjusted relative increases at gestational ages of 34 to 36 weeks (1.0%; 95% CI, 0.6%-1.4%), 37 to 38 weeks (2.3%; 95% CI, 1.9-2.8%) and 42 to 44 weeks (4.2%; 95% CI, 1.5%-7.0%). Mortality at 34 to 36 weeks’ gestation increased by 0.9% (95% CI. 0.2%-1.6%), and another increase was observed at 37 to 38 weeks’ gestation (3.1%; 95% CI, 2.1%-4.1%).
Furthermore, births at 39 to 40 weeks’ gestational age increased while perinatal mortality decreased by –1.3% (95% CI, –1.8% to –0.9%). Ananth and colleagues note that this shift was mostly caused by changes in distribution rather than changes age-specific mortality.
“Improvements in perinatal and neonatal care, particularly quality initiatives almost exclusively centered on the most high-risk infants at a gestational age of less than 32 weeks, are arguably important factors in outcomes for preterm neonates,” the researchers wrote. “Although the proportion of births at 20 to 27 weeks decreased by 8.1%, perinatal and neonatal mortality rates also decreased annually at this gestational age by 0.8% and 0.9%, respectively, after adjustments for confounders.”
“Given the high mortality rates at extremely preterm gestational ages, even a small decrease in the number of deaths will have an influence on overall perinatal mortality,” Ananth and colleagues continued. “Furthermore, improvements in pregnancy dating at these early gestations may have likely shifted a small proportion of births at these low gestational ages to higher gestational ages.” – by Katherine Bortz
Disclosures: The authors report no relevant financial disclosures.
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