Table 3 Mediation of the association between iron deficiency (ferritin <15 μg/L) at enrolment and the birth outcomes birthweight and SGA for pregnant women in the SPCQ treatment group. Madang Province, Papua New Guinea, 2009–2013

Outcome—birthweight (grammes)

Mean difference (95% CI); n = 901

Mean difference (95% CI); n = 901

Mean difference (95% CI); n = 893

Mean difference (95% CI); n = 747

Mean difference (95% CI); n = 815

 Total effect

79.0 (1.0, 157.1)

78.6 (7.5, 149.7)

68.3 (−5.5, 142.1)

46.8 (−35.6, 129.2)

58.7 (−15.5, 132.9)

 Natural direct effect

88.9 (17.2, 160.8)

78.9 (7.8, 150.0)

67.6 (−2.9, 138.0)

40.7 (−39.1, 120.6)

57.2 (−17.3, 131.7)

 Indirect effect

−9.9 (−21.5, 1.6)

−0.3 (−2.0, 1.5)

0.7 (−1.7, 3.1)

6.1 (−3.3, 15.4)

1.5 (−5.8, 8.8)

Outcome—small for gestational age^a

OR (95% CI); n = 589

OR (95% CI); n = 589

OR (95% CI); n = 583

OR (95% CI); n = 486

OR (95% CI); n = 538

 Total effect

0.64 (0.41, 1.00)

0.65 (0.42, 0.99)

0.65 (0.42, 1.00)

0.71 (0.43, 1.17)

0.56 (0.36, 0.89)

 Natural direct effect

0.62 (0.40, 0.95)

0.65 (0.42, 0.99)

0.66 (0.43, 1.02)

0.71 (0.44, 1.15)

0.59 (0.37, 0.93)

 Indirect effect

1.04 (0.93, 1.16)

1.00 (0.99, 1.01)

0.98 (0.90, 1.06)

1.00 (0.86, 1.17)

0.96 (0.89, 1.03)