Association of Temporal Changes in Gestational Age With Perinatal Mortality in the United States, 2007-2015

Abstract

IMPORTANCE Whether the changing gestational age distribution in the United States since 2005 has affected perinatal mortality remains unknown. OBJECTIVE To examine changes in gestational age distribution and gestational age-specific perinatal mortality. DESIGN, SETTING, AND PARTICIPANTS This retrospective cohort study examined trends in US perinatal mortality by linking live birth and infant death data among more than 35 million singleton births from January 1, 2007, through December 31, 2015. EXPOSURES Year of birth and changes in gestational age distribution. MAIN OUTCOMES AND MEASURES Changes in the proportion of births at gestational ages 20 to 27, 28 to 31, 32 to 33, 34 to 36, 37 to 38, 39 to 40, 41, and 42 to 44 weeks; changes in perinatal mortality (stillbirth at Ն20 weeks, and neonatal deaths at <28 days) rates; and contribution of gestational age changes to perinatal mortality. Trends were estimated from log-linear regression models adjusted for confounders. RESULTS Among the 34 236 577 singleton live births during the study period, the proportion of births at all gestational ages declined, except at 39 to 40 weeks, which increased (54.5% in 2007 to 60.2% in 2015). Overall perinatal mortality declined from 9.0 to 8.6 per 1000 births (P < .001). Stillbirths declined from 5.7 to 5.6 per 1000 births (P < .001), and neonatal mortality declined from 3.3 to 3.0 per 1000 births (P < .001). Although the proportion of births at gestational ages 34 to 36, 37 to 38, and 42 to 44 weeks declined, perinatal mortality rates at these gestational ages showed annual adjusted relative increases of 1.0% (95% CI, 0.6%-1.4%), 2.3% (95% CI, 1.9%-2.8%), and 4.2% (95% CI, 1.5%-7.0%), respectively. Neonatal mortality rates at gestational ages 34 to 36 and 37 to 38 weeks showed a relative adjusted annual increase of 0.9% (95% CI, 0.2%-1.6%) and 3.1% (95% CI, 2.1%-4.1%), respectively. Although the proportion of births at gestational age 39 to 40 weeks increased, perinatal mortality showed an annual relative adjusted decline of −1.3% (95% CI, −1.8% to −0.9%). The decline in neonatal mortality rate was largely attributable to changes in the gestational age distribution than to gestational age-specific mortality. CONCLUSIONS AND RELEVANCE Although the proportion of births at gestational age 39 to 40 weeks increased, perinatal mortality at this gestational age declined. This finding may be owing to pregnancies delivered at 39 to 40 weeks that previously would have been unnecessarily delivered earlier, leaving fetuses at higher risk for mortality at other gestational ages.

Association Between Year of Birth and 1-Year Survival Among Extremely Preterm Infants in Sweden During 2004-2007 and 2014-2016

“…28 In parallel, rates of stillbirths increased. 29 The present study showed a survival rate of 77% among all live-born infants at 22-26 weeks' gestational age in 2014-2016, and the stillbirth rate was found to be significantly lower than the rate reported in the rest of Europe. 30 Systematic survival among infants at 22 weeks' gestational age has not been restricted to Swedish hospitals.…”

Epidemiology of late preterm and early term births – An international perspective

“…4) [68]. Whereas this proportion shows declines over that 13-year span in the USA, a recent study revealed that neonatal mortality increased for singleton late preterm and early term births between 2007 and 2015 after adjustment for population characteristics [37]. The authors' interpretation is that declining preterm and early term birth rates, resulting from policies to stop non-medically indicated deliveries, is leading to higher-risk babies being born at these gestational ages.…”

“…The rise was largely accounted for by increases in late preterm births [6], as well as indicated deliveries [12,35]. Rates in the USA then began to decrease when indicated preterm deliveries declined by 17.2% (from 3.9% to 3.2%) between 2005 and 2012 [36] and overall late preterm singleton live births declined from 6.4% to 5.8% between 2007 and 2015 [37]. In Europe, many European countries maintained or reduced their rate of singleton preterm birth [22].…”

Association Between Temporal Changes in Neonatal Mortality and Spontaneous and Clinician-Initiated Deliveries in the United States, 2006-2013

“…[9][10][11] A recent study showed that, among singleton births in the United States, births at late preterm (34-36 weeks), early term (38-39 weeks), and postterm (42-44 weeks) gestations declined between 2007 and 2015. 12 However, perinatal mortality rates at these gestations increased by 1% to 4% annually. In contrast, births at term gestations (39-40 weeks) increased, but mortality rates at this gestation decreased by 1.5%.…”