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

Table 4 Prevalence, odds of underweight (weight-for-age z score < − 2) among children born preterm compared to term-born children, and the population attributable risk of underweight due to preterm birth, estimated using postnatal or gestational age-corrected age from birth to the 48-month follow-up visit

Follow-up visit^a	N	Overall underweight		Term-born children (≥ 37^0/7 weeks)		Preterm-born children (< 37^0/7 weeks)		Odds of underweight among preterm versus term-born children	% Population attributable risk^d
Follow-up visit^a	N	n (%)	P^c	n	Underweight n (%)	n	Underweight n (%)	OR (95% CI)	% Population attributable risk^d
Birth^b
WHO-GS, postnatal age all	4104	284 (6.92)	< 0.001	3625	101 (2.79)	479	183 (38.2)	21.6 (16.5, 28.3)	59.7
IG-NS and IG-VPBR, CA all	4104	151 (3.68)		3625	129 (3.56)	479	22 (4.59)	1.30 (0.82, 2.07)	3.28
3 months
WHO-GS, postnatal age all	3855^e	359 (9.31)	< 0.001	3441	220 (6.39)	414	139 (33.6)	7.40 (5.79, 9.46)	31.3
WHO-GS, CA for CBP, postnatal age for TBC	3855^e	254 (6.59)		3441	220 (6.39)	414	34 (8.21)	1.31 (0.90, 1.91)	2.97
12 months
WHO-GS, postnatal age all	3779	282 (7.46)	< 0.001	3368	214 (6.35)	411	68 (16.5)	2.92 (2.18, 3.92)	14.9
WHO-GS, CA for CBP, postnatal age for TBC	3779	262 (6.93)		3368	214 (6.35)	411	48 (11.7)	1.95 (1.40, 2.71)	8.35
24 months
WHO-GS, postnatal age all	3734	199 (5.33)	0.03	3319	157 (4.73)	415	42 (10.1)	2.27 (1.59, 3.24)	11.2
WHO-GS, CA for CBP, postnatal age for TBC	3734	193 (5.17)		3319	157 (4.73)	415	36 (8.67)	1.91 (1.31, 2.79)	8.48
48 months
WHO-GS, postnatal age all	3612	56 (1.55)	0.24	3216	40 (1.24)	396	16 (4.04)	3.34 (1.85, 6.03)	19.8
WHO-GS, CA for CBP, postnatal age for TBC	3612	53 (1.47)		3216	40 (1.24)	396	13 (3.28)	2.70 (1.43, 5.08)	15.2

CA gestational age-corrected age, CBP children born preterm, CI confidence interval, GA gestational age, IG-NS INTERGROWTH 21st newborn size standards, IG-VPBR INTERGROWTH 21st very preterm size at birth references, OR odds ratio, PAR population attributable risk, TBC term-born children, WHO-GS World Health Organization child growth standards
^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)
^bAt birth, the WHO-GS were applied using postnatal age to all infants born at ≥ 24^0/7 weeks gestational age. For CA strategy, the IG-VPBR were applied to infants born between 24^0/7 and 32^6/7 weeks gestational age and the IG-NS were applied to infants born between 33^0/7 and 43^0/7 weeks gestational age. The gestational age of infants born at > 43^0/7 was truncated 43^0/7 (300 days) to enable application of the IG-NS
^cP values from McNemar’s test for difference in paired proportions when using GA-corrected strategy versus ‘WHO-GS, postnatal age all’ (reference)
^dProportion of all stunting in the population that is attributable to preterm births
^eThe 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)