Table 4.

Weight z--scores and percent of infants weighting less than the 10th percentile*

	All infants	23 to 25 wks	26 to 28 weeks	29 to 31 weeks
Birth vs. FIGR-2013 [21]
median	−0.1	0.1	0.1	−0.9
Average	−0.2	0.0	0.0	−0.9
Standard deviation	0.8	0.8	0.8	0.6
Count	978	225	541	212
% less than 10th percentile	11%	6%	7%	26%
2 weeks postnatal age vs. FIGR-2013
median	−1.0	−0.8	−0.8	−1.6
Average	−1.0	−0.8	−0.8	−1.6
Standard deviation	0.6	0.6	0.6	0.6
Count	862	193	485	184
% less than 10th percentile	31%	22%	20%	68%
37 weeks gestational age vs. FIGR-2013
median	−1.7	−1.9	−1.5	−2.1
Average	−1.7	−1.9	−1.6	−2.1
Standard deviation	0.9	1.0	1.0	1.0
Count	696	169	382	145
% less than 10th percentile	65%	75%	60%	78%
40 weeks gestational age vs. FIGR-2013
median	−1.6	−1.8	−1.3	−1.9
Average	1.3	1.3	1.3	1.2
Standard deviation	−1.5	−1.7	−1.3	−1.8
Count	584	144	316	124
% less than 10th percentile	55%	63%	49%	62%
40 weeks gestational age vs. WHO Growth Standard [16]
median	−0.9	−1.1	−0.7	−1.2
Average	1.1	1.2	1.1	1.1
Standard deviation	−0.8	−1.0	−0.6	−1.1
Count	584	144	315	124
% less than 10th percentile	35%	39%	28%	47%
50 weeks post-menstrual age vs. WHO Growth Standard
median	−1.1	−1.2	−1.0	−1.2
Average	−1.2	−1.3	−1.1	−1.3
Standard deviation	1.2	1.1	1.2	1.0
Count	461	103	256	102
% less than 10th percentile	43%	48%	41%	45%

*Z-scores and assessment of growth restriction (i.e. size less than the 10th percentile) were assigned relative to the fetal-infant growth reference (FIGR)-2013 of intrauterine measures for up to 40 weeks, the World Health Organization (WHO) Growth Standard was used for 40 and 50 weeks.