Table 2.

Association between maternal haemoglobin status at <28 weeks’ gestation and risk of stillbirth at ≥28 weeks’ gestation: National Maternal and Infant Health Survey 1988, United States (Sanderson et al., 1991)

Haemoglobin status*	Black women					Non‐black women
	Total deliveries †	Stillbirth at ≥28 weeks’ gestation ‡				Total deliveries †	Stillbirth at ≥28 weeks’ gestation ‡
		Risk	95% CI	cHR	95% CI		Risk	95% CI	cHR	95% CI
Any anaemia	250	0.40	0.26, 0.54	0.87	0.58, 1.30	72	0.26	0.25, 0.27	0.97	0.50, 1.47
Mild	199	0.42	0.26, 0.58	0.94	0.61, 1.45	60	0.22	0.09, 0.35	0.84	0.44, 1.57
Moderate or severe	51	0.31	0.01, 0.61	0.64	0.23, 1.73	12	0.63	0.01, 14.4	3.82	1.00, 14.6
Normal haemoglobin	1832	0.52	0.48, 0.56	1.00	Ref	3158	0.29	0.15, 0.43	1.00	Ref
High haemoglobin	48	1.20	0.42, 1.98	1.94	0.94, 3.98	214	0.30	0.21, 0.39	0.95	0.68, 1.35

^* 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.

^† Unweighted number of deliveries.

^‡ Risk of stillbirth is expressed per 1000 live births plus stillbirths (≥28 weeks’ gestation).

cHR, crude hazards ratio; CI, confidence intervals; Ref, reference.