Table 3.

Adjusted hazard ratio* for stillbirth at ≥28 weeks’ gestation by haemoglobin status at <28 weeks’ gestation: National Maternal and Infant Health Survey 1988, United States (Sanderson et al., 1991)

Timimng of haemoglobin measurement	Haemoglobin status†
	Any anaemia			Mild anaemia			Moderate or severe anaemia			Normal haemoglobin			High haemoglobin
	Total deliveries†	HR	95%CI	Totaldeliveries†	HR	95%CI	Totaldeliveries†	HR	95%CI	Totaldeliveries†	HR	95%CI	Totaldeliveries†	HR	95% CI
Black women
<28 weeks	250	1.05	0.68, 1.61	199	1.09	0.68, 1.74	51	0.86	0.32, 2.34	1832	1.00	Ref	48	2.02	0.96, 4.23
<13 weeks	106	0.99	0.16, 2.12	56	1.07	0.50, 2.31	16	‡		696	1.00	Ref	18	3.67	0.92, 14.6
13–27 weeks	144	1.12	0.65, 1.92	143	1.11	0.61, 2.04	35	1.14	0.41, 3.17	1136	1.00	Ref	30	2.69	0.69, 10.5
Non‐black women
<28 weeks	72	0.80	0.41, 1.56	60	0.65	0.31, 1.34	12	4.41	1.02, 19.0	3158	1.00	Ref	214	0.95	0.63, 1.43
<13 weeks	31	0.67	0.25, 1.77	26	0.49	0.16, 1.54	5	2.87	0.33, 25.2	994	1.00	Ref	109	0.70	0.39, 1.25
13–27 weeks	41	1.09	0.46, 2.59	34	0.90	0.35, 2.27	7	9.40	1.50, 59.0	2164	1.00	Ref	105	1.62	0.72, 3.65

^* Hazard ratios were adjusted for maternal age, parity, marital status, maternal education, cocaine use during pregnancy, pre‐pregnancy body mass index, prenatal iron supplementation, and iron/multivitamin use during pregnancy, and pre‐eclampsia/eclampsia.

^† Maternal haemoglobin concentrations during the first and second trimesters were classified as anaemia (haemoglobin <11.0 g dL⁻¹ and < 10.5 g dL⁻¹, respectively), mild anaemia (10.0 to <11.0 g dL⁻¹ and 9.5 to <10.5 g dL⁻¹), moderate anaemia (9.0 to <10.0 g dL⁻¹ and 8.5 to < 9.5 g dL⁻¹) and high haemoglobin (≥14.6 g dL⁻¹ in either trimester). Normal haemoglobin includes women with neither anaemia nor high haemoglobin.

^‡ Number of stillbirths was too few for meaningful analysis.

HR, hazard ratios; CI, confidence intervals; Ref, reference.