TABLE 2.

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

				Low hemoglobin2				High hemoglobin2
Study (ref), year	Hemoglobin cutoffs	n	Country or study type	LBW	PTB	SGA	Stillbirth	LBW	PTB	SGA	Stillbirth
Abeysena et al. (20), 2010	110, >139 g/L	817	Sri Lanka	o	o	o		↑	o	o
Alwan et al. (21), 2015	<110 g/L	362	England		o	(↑)
Chang et al. (5), 2003	<105, >120 g/L	918	United States	o	o	o		↑	↑	o
Gonzales et al. (4), 2009	<110, >129 g/L	35,449	Peru		↑	↑	↑		↑	↑	↑
Hämäläinen et al. (11), 2003	<100 g/L	597 cases, 22,202 controls	Finland	o	o	o	o
Little et al. (22), 2005	No definition	222,614	England				o				o
Scanlon et al. (14), 2000	<−1, >1 SD from the reference group	173,031	United States		↑	o			o	↑
Scholl et al. (23), 1992	<105 g/L	826	United States	o	o	o
Tomashek et al. (16), 2006	<105, ≥146 g/L	1375 cases, 4199 controls	United States				(↑)				(↑)
Verhoeff et al. (24), 2001	<80 g/L	1423	Malawi		o	↑
Xiong et al. (25), 2000	<100–110 g/L	NA	Meta-analysis	o	↑	o
Zhang et al. (17), 2009	<100, ≥120 g/L	160,700	China		o				o
Zhang et al. (18), 2009	<100, ≥120 g/L	1354 cases, 163,313 controls	China				o				o
Zhou et al. (19), 1998	<100, ≥120 g/L	829	China	o	o	o		o	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; NA, not applicable; 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.