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

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

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
  1. 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)
  2. CI confidence interval, LBW low birth weight, OR odds ratio, PTB preterm birth