Mortality in infants affected by preterm birth and severe small-for-gestational age birth weight

Background — Few studies evaluated neonatal mortality in the combined presence of preterm birth (PTB) and small for gestational age birthweight (SGA). None differentiated between infants with and without anomalies, considered births starting at 23 weeks’ gestation, or defined SGA at a more pathological cut-point below the 5th percentile.

Methods — We completed a population-based cohort study within the province of Ontario,Canada, 2002-2015. Included were 1,676,110 singleton hospital live births at 23-42 weeks’ gestation. Modified Poisson regression compared rates and relative risks (RR) of neonatal mortality among those with i) PTB at 23-36 weeks’ gestation and concomitant severe SGA (PTB-SGA); ii) PTB at 23-36 weeks’ without severe SGA; iii) term birth with severe SGA; each relative to iv) neither. RRs were adjusted for maternal age, and also stratified by several demographic variables.

Results — Relative to a neonatal mortality rate of 0.6 per 1000 in term infants without severe SGA, the rate was 2.8 per 1000 among term births with severe SGA (adjusted RR [aRR] 4.6, 95%-CI 4.0-5.4), 22.9 per 1000 for PTB without severe SGA (aRR 38.3, 95% CI 35.4 to 41.4) and 60.0 per 1000 for PTB-SGA (aRR 96.7, 95% CI 85.4-109.5). Stratification by demographic factors showed a persistence of this pattern of neonatal death. Restricting the sample to births at ≥ 24 weeks, or newborns without a congenital or chromosomal anomaly, also demonstrated the same pattern.

Conclusions — Methods to detect or prevent PTB or SGA should focus on PTB-SGA, which serves as a useful perinatal surveillance indicator.