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Table 2 Regression modelling of transformed abdominal circumference and estimated fetal weight in relation to gestational age

From: Unconditional and conditional standards for fetal abdominal circumference and estimated fetal weight in an ethnic Chinese population: a birth cohort study

  Step Parameter Both genders pooled Male Female
Transformed AC Fractional polynomial transformation of GA p 1 -2 -2 -2
p 2 1 1 1
a 1 -168.4982 -164.9962 -172.1061
a 2 0.0297 0.0297 0.0298
Mixed-effects model regressing log(AC) on f(GA) = GA− 2 + (a2/a1)GA b 0 4.8170 4.8201 4.8114
b 1 -168.4671 -165.0468 -172.0514
var(β0i) 0.0012 0.0009 0.0012
var(β1i) 18.5802 32.9797 0.0999
cov(β0i, β1i) 0.0490 0.0747 -0.0108
var(e ij ) 0.0008 0.0008 0.0009
Transformed EFW Fractional polynomial transformation of GA p 1 0.5 0.5 0.5
p 2 2 2 2
a 1 -0.1176268 -0.1166731 -0.1186321
a 2 0.0796 × 10-3 0.0783 × 10-3 0.0809 × 10-3
Mixed-effects model regressing EFW-0.1 on f(GA) = GA0.5 + (a2/a1)GA2 b 0 1.0573 1.0528 1.0623
b 1 -0.1176 -0.1167 -0.1186
var(β0i) 7.370 × 10-6 3.004 × 10-4 16.70 × 10-6
var(β1i) 1.668 × 10-4 14.2 × 10-6 7.74 × 10-12
cov(β0i, β1i) -0.335 × 10-4 -0.64 × 10-4 -1.12 × 10-8
var(e ij ) 6.290 × 10-6 5.43 × 10-6 7.13 × 10-6
  1. AC abdominal circumference, EFW estimated fetal weight, GA gestational age in exact weeks