Supplemental Table 1.

Variance components analysis^a for 3 umbilical artery Doppler indices

	Pulsatility index	Resistance index	Systolic/diastolic ratio
Number of measures	1021	1020	1022
Variance between study sites	2.8	6.5	5.6
Variance between individuals within a site	25.4	22.9	20.9
Residual variance	71.8	70.6	73.5

Models included women with 3 or more scans performed between 23 and 40 weeks’ gestation (316 women and 1023 scans were available for these analyses).

Drukker et al. International gestational age-specific centiles for umbilical artery Doppler indices: a longitudinal prospective cohort study of the INTERGROWTH-21^st Project. Am J Obstet Gynecol 2020.

^aFrom multilevel mixed-effects models fitted with random intercepts for the study-site and individual levels (with individuals nested within sites) and adjustment for gestational age (treated as fixed effect).