TABLE 1.

Associations of a low or high hemoglobin concentration in the first trimester with birth outcomes¹

				Low hemoglobin2				High hemoglobin2
Study (ref), year	Hemoglobin cutoffs	n	Country	LBW	PTB	SGA	Stillbirth	LBW	PTB	SGA	Stillbirth
Delpisheh et al. (10), 2008	<110 g/L	270	England			↑
Hämäläinen et al. (11), 2003	<100 g/L	597 cases, 22,202 controls	Finland	↑	o	o	o
Maghsoudlou et al. (12), 2016	<110, ≥140 g/L	495 cases, 2888 controls	Iran				o				o
Ren et al. (13), 2007	<110, ≥120 g/L	88,149	China	↑	↑	↑		o	o	o
Scanlon et al. (14), 2000	<−1, >1 SD from the reference group	173,031	United States		↑	o			o	↑
Stephansson et al. (15), 2000	≤115, ≥146 g/L	702 cases, 702 controls	Sweden				(↑)				(↑)
Tomashek et al. (16), 2006	<110, ≥146 g/L	1375 cases, 4199 controls	United States				o				(↑)
Zhang et al. (17), 2009	<90, ≥130 g/L	160,700	China		(↑)				↓
Zhang et al. (18), 2009	<90, ≥120 g/L	1354 cases, 163,313 controls	China				(↑)				o
Zhou et al. (19), 1998	<110, ≥120 g/L	829	China	↑	↑	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. LBW, low birth weight; PTB, preterm birth; ref, reference; SGA, small-for-gestational-age.

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