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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