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UBC Theses and Dissertations

Temporal trends in neonatal mortality and morbidity following spontaneous and clinician-initiated preterm birth in Canada and the United States Richter, Lindsay Louise


Preterm birth (PTB; <37 weeks’ gestation) is the leading cause of neonatal mortality and morbidity. After a decade of increase, the PTB rate has declined in the United States since 2006. In Canada, PTB rates have remained stable, despite the rise in clinician-initiated deliveries at late preterm (34-36 weeks) since 2006. I examined temporal trends in the rates of spontaneous and clinician-initiated singleton PTB and assessed concomitant changes in neonatal mortality and severe morbidity. I conducted two retrospective population-based studies included singleton births (24-45 weeks) in Washington State (WA), U.S.A., 2004-2013, using birth certificate data linked to hospitalization records (N=754,763), and in Canada (excluding Quebec), 2009/2010-2015/2016, using national data on all hospital births (N=1,887,362). Primary outcomes were neonatal mortality and a composite outcome including death and/or severe neonatal morbidity (identified by diagnostic codes; definitions varied in both studies). Statistical significance was assessed using the Cochran-Armitage test for trend. Logistic regression yielded adjusted odds ratios (AOR) per 1-year change and 95% confidence intervals (CI). The singleton PTB rate in WA declined from 7.3% in 2004-2006 to 7.0% in 2011-2013 (n=52,014), predominantly due to declines in spontaneous labour and PPROM. The proportion of clinician-initiated PTBs increased from 37.7% to 40.7% in WA (p=0.004). Similarly, clinician-initiated deliveries increased from 31.0% in 2009/2010 to 37.9% in 2015/2016 in Canada (p<0.001). The corresponding decrease in spontaneous PTBs resulted in a stable PTB rate (6.2%; n=117,114) across Canada. Overall, neonatal mortality remained unchanged; 1.3% in WA and 1.1% in Canada. In subgroup analysis, neonatal mortality decreased at 32-33 weeks (AOR:0.85, CI:0.74-0.97) and increased at 34-36 weeks (AOR:1.10, CI:1.01-1.20) following clinician-initiated delivery in WA; mortality decreased at 28-33 weeks (AOR:0.91, CI:0.86-0.97) after spontaneous PTB in Canada. The composite outcome of neonatal mortality/severe morbidity increased from 7.9% to 11.9% (AOR:1.06, CI:1.05-1.08) in WA, mainly at 34-36 weeks. Neonatal mortality/severe morbidity decreased from 12.7% to 12.2% (AOR:0.98, CI:0.97-0.99) in Canada, particularly in clinician-initiated late PTB. The endured increase in clinician-initiated PTB was not associated with increased adverse neonatal outcomes in Canada. The increase in adverse neonatal health outcomes in Washington State, particularly at late preterm, warrant further investigation.

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