Neonatal mortality risk for vulnerable newborn types in 15 countries using 125.5 million nationwide birth outcome records, 2000–2020

Objective
To compare neonatal mortality associated with six novel vulnerable newborn types in 125.5 million live births across 15 countries, 2000–2020.

Design
Population-based, multi-country study.

Setting
National data systems in 15 middle- and high-income countries.

Methods
We used individual-level data sets identified for the Vulnerable Newborn Measurement Collaboration. We examined the contribution to neonatal mortality of six newborn types combining gestational age (preterm [PT] versus term [T]) and size-for-gestational age (small [SGA], 90th centile) according to INTERGROWTH-21st newborn standards. Newborn babies with PT or SGA were defined as small and T + LGA was considered as large. We calculated risk ratios (RRs) and population attributable risks (PAR%) for the six newborn types.

Main outcome measures
Mortality of six newborn types.

Results
Of 125.5 million live births analysed, risk ratios were highest among PT + SGA (median 67.2, interquartile range [IQR] 45.6–73.9), PT + AGA (median 34.3, IQR 23.9–37.5) and PT + LGA (median 28.3, IQR 18.4–32.3). At the population level, PT + AGA was the greatest contributor to newborn mortality (median PAR% 53.7, IQR 44.5–54.9). Mortality risk was highest among newborns born before 28 weeks (median RR 279.5, IQR 234.2–388.5) compared with babies born between 37 and 42 completed weeks or with a birthweight less than 1000 g (median RR 282.8, IQR 194.7–342.8) compared with those between 2500 g and 4000 g as a reference group.

Conclusion
Preterm newborn types were the most vulnerable, and associated with the highest mortality, particularly with co-existence of preterm and SGA. As PT + AGA is more prevalent, it is responsible for the greatest burden of neonatal deaths at population level.