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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