TABLE 4.

Associations of low or high iron status, by trimester, with birth outcomes¹

				Low iron status2				High iron status2
Study (ref), year	Iron status cutoffs	n	Country or study type	LBW	PTB	SGA	Stillbirth	LBW	PTB	SGA	Stillbirth
First trimester
Alwan et al. (21), 2015	SF <15 μg/L	362	England		o	↑
Khambalia et al. (9), 2015	SF <12 μg/L, sTfR ≥21.0 nmol/L, SF ≥75th percentile	2254	Australia		—				↑
Khambalia et al. (32), 2016	SF <12 μg/L, sTfR ≥21.0 nmol/L, TBI <0 mg/kg	4420	Australia		o	o
Second trimester
Goldenberg et al. (33), 1996	SF by quartiles	580	United States	o	o			↑	↑
Scholl et al. (23), 1992	SF <12 μg/L	826	United States	↑	↑	o
Scholl (34), 1998	SF ≥90th percentile	1162	United States					o	o
Tamura et al. (35), 1996	SF median cutoff	31 cases, 63 controls	United States						↑
Verhoeff et al. (24), 2001	EP >2.7 μg ZPP/g hemoglobin and MCHC <32 g/dL	1423	Malawi		o	o
Third trimester
Goldenberg et al. (33), 1996	SF by quartiles	580	United States	o	o			↑
Lao et al. (36), 2000	SF by quartiles	488	China		o				↑
Scholl (34), 1998	SF ≥90th percentile	1162	United States					↑	↑
Verhoeff et al. (24), 2001	EP >2.7 μg ZPP/g hemoglobin and MCHC <32 g/dL	1423	Malawi		o	o

¹↑ indicates a positive association (higher OR or RR of birth outcome), P < 0.05; (↑) indicates a marginally significant positive association, 0.05 ≥ P < 0.10; ↓ indicates a negative association (lower OR or RR for birth outcome), P < 0.05; (↓) indicates a marginally significant negative association, 0.05 ≥ P < 0.10; o indicates no association; a blank cell indicates the relation was not examined. EP, erythrocyte protoporphyrin; LBW, low birth weight; MCHC, mean corpuscular hemoglobin concentration; PTB, preterm birth; ref, reference; SF, serum ferritin; SGA, small-for-gestational-age; sTfR, soluble transferrin receptor; TBI, total body iron stores; ZPP, zinc protoporphyrin.

²Low and high iron status as defined by each study. Cutoffs used for each definition are provided in the second column.