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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 12 countries. Sample 119,644,788 total births from 22+0 to 44+6 weeks gestation identified from 2000 to 2020. Methods We included 605,557 stillbirths from 22+0 weeks gestation from 12 countries. We classified all births, including stillbirths, by six "newborn types" based on gestational age information (preterm, PT, <37+0 weeks vs 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 605,557 (0.50%) of the 119,644,788 total births resulted in stillbirth after 22+0 weeks. Most stillbirths (74.3%) were preterm. Around 21.0% were SGA types (PT+SGA (16.0%), T+SGA (5.0%)) and 14.3% were LGA types (PT+LGA (10.1%), T+LGA (4.2%)). The median rate ratio (RR) for stillbirth was highest in PT+SGA babies (RR=78.8, interquartile range (IQR), 68.2, 111.5) followed by PT+AGA (RR=24.5, IQR, 19.3, 29.4), PT+LGA (RR=23.0, IQR,13.7, 29.0) and T+SGA (RR=5.5, IQR, 5.0, 6.0) compared with T+AGA. Stillbirth rate ratios were similar for T+LGA vs T+AGA (RR=0.7, IQR, 0.7, 1.1). At the population level, 21.5% 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 were 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, and also patterns in lower-income contexts, especially those with higher rates of intrapartum stillbirth and SGA. Funding The Childrens Investment Fund Foundation, 1803-02535 Keywords newborn, stillbirths, premature birth, preterm, pregnancy, gestational age TWEETABLE ABSTRACT OF 110 CHARACTERS Word count 3,482

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