Table 2.

Duration of sleep stages and characteristics of sleep spindle patterns depending on infant iron status^*

	Iron-deficient anemic	Non-anemic	P-value	Significant covariates
Waking prior to nap
Duration of stage (min)	200.4 ± 13.9	251.1 ± 11.3	0.01	Birth weight, WAZ
NREM stage 2
Duration of stage (min)	25.8 ± 5.9	30.5 ± 6.1	0.88	Mother’s IQ
Spindle index (spindles/min)	2.4 ± 0.2	2.9 ± 0.2	0.05	Age
Spindle duration (s)	1.9 ± 0.1	2.0 ± 0.1	0.39
Inter-spindle interval (s)	27.9 ± 3.3	19.6 ± 1.7	0.02	Age
Spindle frequency (Hz)	12.3 ± 0.1	13.4 ± 0.1	<0.0001
SWS
Duration of stage (min)	37.7 ± 4.6	30.5 ± 5.0	0.23	Mother’s IQ
Spindle index (spindles/min)	2.0 ± 0.2	2.8 ± 0.2	0.001	Gender
Spindle duration (s)	1.9 ± 0.1	2.0 ± 0.1	0.72	WAZ
Inter-spindle interval (s)	31.3 ± 2.7	21.0 ± 2.2	0.009
Spindle frequency (Hz)	12.3 ± 0.1	13.2 ± 0.1	<0.0001

^*Values are mean ± SE