Stillbirths: Contribution of preterm birth and size-for-gestational age for 125.4 million total births from nationwide records in 13 countries, 2000-2020

Abstract

Objective: To examine the contribution of preterm birth and size-for-gestational age in stillbirths using six 'newborn types'.

Design: Population-based multi-country analyses.

Setting: Births collected through routine data systems in 13 countries.

Sample: 125 419 255 total births from 22⁺⁰ to 44⁺⁶ weeks' gestation identified from 2000 to 2020.

Methods: We included 635 107 stillbirths from 22⁺⁰ weeks' gestation from 13 countries. We classified all births, including stillbirths, into six 'newborn types' based on gestational age information (preterm, PT, <37⁺⁰ weeks versus term, T, ≥37⁺⁰ weeks) and size-for-gestational age defined as small (SGA, <10th centile), appropriate (AGA, 10th-90th centiles) or large (LGA, >90th centile) for gestational age, according to the international newborn size for gestational age and sex INTERGROWTH-21st standards.

Main outcome measures: Distribution of stillbirths, stillbirth rates and rate ratios according to six newborn types.

Results: 635 107 (0.5%) of the 125 419 255 total births resulted in stillbirth after 22⁺⁰ weeks. Most stillbirths (74.3%) were preterm. Around 21.2% were SGA types (PT + SGA [16.2%], PT + AGA [48.3%], T + SGA [5.0%]) and 14.1% were LGA types (PT + LGA [9.9%], T + LGA [4.2%]). The median rate ratio (RR) for stillbirth was highest in PT + SGA babies (RR 81.1, interquartile range [IQR], 68.8-118.8) followed by PT + AGA (RR 25.0, IQR, 20.0-34.3), PT + LGA (RR 25.9, IQR, 13.8-28.7) and T + SGA (RR 5.6, IQR, 5.1-6.0) compared with T + AGA. Stillbirth rate ratios were similar for T + LGA versus T + AGA (RR 0.7, IQR, 0.7-1.1). At the population level, 25% of stillbirths were attributable to small-for-gestational-age.

Conclusions: In these high-quality data from high/middle income countries, almost three-quarters of stillbirths were born preterm and a fifth small-for-gestational age, with the highest stillbirth rates associated with the coexistence of preterm and SGA. Further analyses are needed to better understand patterns of gestation-specific risk in these populations, as well as patterns in lower-income contexts, especially those with higher rates of intrapartum stillbirth and SGA.

Keywords: gestational age; newborn; pregnancy; premature birth; preterm; stillbirths.