Hemoglobin Concentration and Pregnancy Outcomes: A Systematic Review and Meta-Analysis

Table 2

Association between hemoglobin concentration and pregnancy outcomes.

Outcome	Trimester	Number of studies	Number of subjects	Hemoglobin cutoff	Pooled OR	95% CI	𝐼^2	95% CI
Preterm birth	First			<9	1.72	1.30–2.26	4	0–45
		11	192,870	<10	1.33	1.17–1.52	10	0–59
				<11	1.10	1.02–1.19	5	0–44
	Reference			11–13.9	1.00
				≥14	0.99	0.86–1.14	31	0–74
	Third			<9	3.41	1.38–8.42	0	0–6
		7	29,879	<10	2.64	1.19–5.86	0	0–45
				<11	1.18	0.83–1.70	45	0–83
	Reference			11–13.9	1.00
					≥14	0.50	0.26–0.97	0	0–48
Low birth weight	First			<9	2.14	1.57–2.91	0	0–11
		10	106,892	<10	1.57	1.30–1.90	7	0–43
				<11	1.17	1.03–1.32	2	0–38
	Reference			11–13.9	1.00
				≥14	0.89	0.70–1.13	44	0–84
	Third	6	9,285	<10	3.61	1.83–7.12	0	0–50
				<11	1.30	1.08–1.58	58	0–91
	Reference			11–13.9	1.00
					≥14	0.59	0.14–2.50	0	0
Small for gestational age	First			<9	1.37	0.73–2.56	7	0–60
		6	94,280	<10	1.26	1.09–1.45	1	0–47
				<11	1.14	1.05–1.24	2	0–55
	Reference			11–13.9	1.00
				≥14	0.97	0.84–1.12	20	0–68