Temporal Trends in Preterm Birth Associated With Hypertensive Disorders of Pregnancy in Victoria, Australia: A Population-Based Interrupted Time-Series Study.

摘要

OBJECTIVES: Hypertensive disorders of pregnancy (HDP) are a leading reason for medically indicated preterm birth (PTB), yet their contribution to population-level PTB trends is poorly understood. We examined temporal trends in PTB overall and HDP-associated PTB in Victoria over an 11-year period spanning the COVID-19 pandemic, and distinguished changes in HDP prevalence from changes in preterm delivery among affected pregnancies. STUDY TYPE: Population-based interrupted time-series study using seasonal autoregressive integrated moving average (SARIMA) models, with July 2018 (launch of a national preterm birth prevention program) pre-specified as a temporal reference point. SETTING: All hospitals in Victoria, Australia. PARTICIPANTS: 779,325 singleton births at ≥ 20 weeks' gestation between 1 January 2012 and 31 March 2022. MAIN OUTCOME MEASURES: Monthly rates (per 1000 singleton births) of overall PTB, HDP and HDP-associated PTB. Decomposition analyses separated changes in HDP prevalence from changes in preterm delivery among affected pregnancies. RESULTS: Overall PTB was lower after July 2018 (5.8%-5.6%), while HDP prevalence increased (6.4%-7.0%). HDP-associated PTB increased before mid-2018 (+0.75 per 1000 births per month; 95% confidence interval [CI], 0.50-1.00) but declined thereafter (-1.12 per 1000 births per month; 95% CI, -1.88 to -0.36). This reversal was driven predominantly by reduced iatrogenic PTB with HDP; spontaneous PTB with HDP showed no significant change. Despite rising HDP prevalence, decomposition analyses estimated 89 fewer HDP-associated PTB cases than expected under pre-2018 patterns, reflecting a decline in the proportion of HDP pregnancies delivered preterm. PTB without HDP showed no significant temporal change. CONCLUSION: PTB among HDP-complicated pregnancies declined despite increasing HDP prevalence, consistent with a shift towards later gestational age at delivery rather than reduced disease incidence. These findings may reflect improvements in care and demonstrate that reductions in iatrogenic PTB are achievable even as major risk factors become more prevalent. The Known: Preterm birth (birth before 37 weeks of pregnancy) is a major cause of infant illness and death. High blood pressure during pregnancy is a common and serious condition and the leading reason for medically indicated, planned preterm birth. The New: Using data from all Victorian singleton births between 2012 and 2022, we found that high blood pressure during pregnancy became more common, but preterm birth among affected pregnancies declined. This was mainly due to fewer medically recommended preterm births, while preterm birth after spontaneous preterm labour showed little change. The Implications: Although high blood pressure during pregnancy is increasing, more affected pregnancies are now reaching full‐term gestation, suggesting improved outcomes for mothers and newborns. This reduction in preterm birth with hypertension may reflect changes in the severity of the hypertensive disorders, changes in clinical care or both.