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Table 2 Weight-for-age z scores from birth to 48 months estimated using either postnatal age in the application of the World Health Organization child growth standards for all children, or using the INTERGROWTH 21st very preterm size at birth references, the newborn size standards at birth, and gestational age-corrected age for preterm-born children postnatally

From: Effect of correcting for gestational age at birth on population prevalence of early childhood undernutrition

Follow-up visita n Excluded n Flagged Obsc Mean ± SDd Median (1st, 99th) Term-born children (≥ 370/7 weeks) Preterm-born children (< 370/7 weeks) Mean difference in WAZ among term versus preterm-born
No data Ineligible for analysis n Mean ± SD n Mean ± SD Mean difference (95% CI) P valuee
Birthb
 WHO-GS, postnatal age all 4104 1 2 14 − 0.30 ± 1.20 − 0.20 (− 4.35, 1.94) 3625 − 0.09 ± 0.93 479 − 1.93 ± 1.65 1.85 (1.69, 2.0) < 0.001
 IG-NS and IG-VPBR, CA all 4104 1 2 0 0.03 ± 1.08 0.06 (− 2.48, 2.32) 3625 0.01 ± 1.07 479 0.18 ± 1.12 − 0.17 (− 0.27, − 0.06) 0.003
3 months
 WHO-GS, postnatal age all 3855 8 2f 6 − 0.50 ± 1.16 − 0.40 (− 3.97, 1.87) 3441 − 0.38 ± 1.04 414 − 1.56 ± 1.49 1.19 (1.04, 1.34) < 0.001
 WHO-GS, CA for CBP, postnatal age for TBC 3855 8 2f 0 − 0.37 ± 1.06 − 0.32 (− 3.30, 1.95) 3441 − 0.38 ± 1.04 414 − 0.29 ± 1.23 − 0.08 (− 0.21, 0.04) 0.19
12 months
 WHO-GS, postnatal age all 3779 25 0 1 − 0.25 ± 1.23 − 0.24 (− 3.27, 2.61) 3368 − 0.18 ± 1.20 411 − 0.79 ± 1.35 0.61 (0.47, 0.74) < 0.001
 WHO-GS, CA for CBP, postnatal age for TBC 3779 25 0 1 − 0.22 ± 1.22 − 0.21 (− 3.20, 2.62) 3368 − 0.18 ± 1.20 411 − 0.54 ± 1.32 0.36 (0.23, 0.50) < 0.001
24 months
 WHO-GS, postnatal age all 3734 14 0 4 − 0.11 ± 1.21 − 0.13 (− 3.06, 2.86) 3319 − 0.06 ± 1.19 415 − 0.57 ± 1.29 0.52 (0.39, 0.65) < 0.001
 WHO-GS, CA for CBP, postnatal age for TBC 3734 14 0 4 − 0.10 ± 1.21 − 0.11 (− 2.96, 2.86) 3319 − 0.06 ± 1.19 415 − 0.41 ± 1.29 0.36 (0.22, 0.49) < 0.001
48 months
 WHO-GS, postnatal age all 3612 1 0 11 0.43 ± 1.26 0.30 (− 2.22, 4.21) 3216 0.47 ± 1.24 396 0.05 ± 1.28 0.42 (0.29, 0.55) < 0.001
 WHO-GS, CA for CBP, postnatal age for TBC 3612 1 0 12 0.44 ± 1.25 0.31 (− 2.16, 4.23) 3216 0.47 ± 1.24 396 0.14 ± 1.29 0.33 (0.20, 0.47) < 0.001
  1. CA gestational age-corrected age, CBP children born preterm, GA gestational age, IG-NS INTERGROWTH-21st newborn size standards, IG-VPBR INTERGROWTH 21st very preterm size at birth references, SD standard deviation, TBC term-born children, WHO-GS World Health Organization child growth standards
  2. aChild postnatal age during follow-up visits ranged from: 3 months (± 1 month); 12 months (± 2 months); 24 months (± 2 months); 48 months (± 6 months)
  3. bAt birth, WHO-GS were applied using postnatal age to all infants born at ≥ 240/7 weeks gestational age. For CA strategy, the IG-VPBR were applied to infants born between 240/7 to 326/7 weeks gestational age and the IG-NS were applied to infants born between 330/7 and 430/7 weeks gestational age. The gestational age of infants born at > 430/7 was truncated 430/7 (300 days) to enable application of the IG-NS
  4. cWeight-for-age z scores < −6SD or > 5SD were flagged as “biologically implausible” values by the World Health Organization child growth standards macro. These values were not excluded from summary estimates
  5. dP values for difference in paired means estimated using a paired sample t-test at each visit were P < 0.001 at all follow-up visits
  6. eP value for mean difference in weight-for-age z scores among term versus preterm-born children was estimated using independent sample t-test with unequal variances
  7. fThe WHO-GS could not be applied to two infants who had a corrected age of < 0 at the 3-month visit and therefore were excluded from the ‘WHO-GS, postnatal age all’ strategy as well (inferences were unchanged when these two infants were included)