Iron deficiency during pregnancy is associated with a reduced risk of adverse birth outcomes in a malaria-endemic area in a longitudinal cohort study

Table 2 Associations between iron deficiency and birth outcomes and effect modification by gravidity

Birth weight (grams)
Iron stores	Unadjusted mean difference (95% CI); p	Adjusted mean difference (95% CI); p
Ferritin, μg/L (log₂)¹	−72 (−113, −30); 0.001	−63 (−103, −23); 0.002
		Primigravid	Multigravid
		−114 (−173, −55); <0.001	−20 (−74, 33); 0.457
Iron deficiency
Iron replete	Reference group	Reference group
Iron deficient	204 (89, 320); 0.001	230 (118, 342); <0.001
		Primigravid	Multigravid
		351 (188, 514); <0.001	125 (−28, 277); 0.108
Low birth weight (<2500 g)
Iron stores	Unadjusted OR (95% CI); p	Adjusted OR (95% CI); p
Iron deficiency
Iron replete	Reference group	Reference group
Iron deficient	0.34 (0.18, 0.65); 0.001	0.32 (0.16, 0.64); 0.001
		Primigravid	Multigravid
		0.26 (0.10, 0.66); 0.005	0.42 (0.15, 1.20); 0.105
Preterm birth (<37 weeks)
Iron stores	Unadjusted OR (95% CI); p	Adjusted OR (95% CI); p
Ferritin, μg/L (log₂)¹	1.13 (0.91, 1.41); 0.254	1.06 (0.84, 1.35); 0.605
		Primigravid	Multigravid
		1.20 (0.86, 1.66); 0.280	0.93 (0.65, 1.33); 0.681
Iron deficiency
Iron replete	Reference group	Reference group
Iron deficient	0.60 (0.33, 1.10); 0.098	0.57 (0.30, 1.09); 0.089
		Primigravid	Multigravid
		0.39 (0.16, 0.97); 0.042	0.86 (0.32, 2.30); 0.767

Multivariable models including confounding variables (gravidity, gestational age, education, mid-upper arm circumference and smoking), and sex of the newborn (linear models only). ¹Ferritin transformed to log base 2 due to positively skewed distribution; coefficients are, therefore, for the absolute or relative change in outcome associated with each twofold increase in ferritin concentration. p values for gravidity interaction parameters are 0.019 (ferritin, birth weight), 0.042 (iron deficiency, birth weight), 0.500 (iron deficiency, LBW), 0.299 (ferritin, PTB) and 0.236 (iron deficiency, PTB)
CI confidence interval, LBW low birth weight, OR odds ratio, PTB preterm birth