Robertson's Method for Amniotic Fluid Bilirubin

Line

Zones

Weeks

Line Equation LOG10(delta OD450) =

1a

A and B1

17 to 22

0.06

1b

A and B1

22 to 27

(-0.002 * (week gestation)) + 0.113

2

B1 and C1

17 to 27

(-0.001 * (week gestation)) + 0.117

3a

C1 and F1

17 to 20

(0.018 * (week gestation)) - 0.212

3b

C1 and F1

20 to 23

( 0.015* (week gestation)) - 0.145

4

C1 and D1

23 to 27

(-0.019 * (week gestation)) + 0.631

5

D1 and F1

23 to 27

(0.004 * (week gestation)) + 0.114

6

F1 and G1

16 to 27

(0.015 * (week gestation)) - 0.093

7a

G1 and X1

16 to 22

(0.017 * (week gestation)) - 0.067

7b

G1 and X1

22 to 27

(0.012 * (week gestation)) + 0.036

Line

Zones

Weeks

Line Equation for delta OD450

8

A and B2

27 to 30

(-0.013 * (week gestation)) + 0.39

9a

B2 and C2

27 to 31

(-0.010 * (week gestation)) + 0.36

9b

B2 and C2

31 to 36

(-0.005 * (week gestation)) + 0.205

10a

C2 and D2

27 to 34

(-0.010 * (week gestation)) + 0.395

10b

C2 and D2

34 to 36

(-0.008 * (week gestation)) + 0.310

11a

D2 and E

27 to 35

(-0.019 * (week gestation)) + 0.721

11b

D2 and E

35 to 37

(-0.010 * (week gestation)) + 0.398

12a

E and F2G2

27 to 34

(-0.011 * (week gestation)) + 0.524

12b

E and F2G2

34 to 37

(-0.007 * (week gestation)) + 0.384

13

F2G2 and X2

27 to 34

(-0.023 * (week gestation)) + 0.977

Weeks

Line Relation

Zone

Action

18-23

below 1

A

repeat 4 weeks, deliver at term

between 1 and 2

B1

repeat 4 weeks

between 2 and 3

C1

repeat 3 weeks

between 3 and 6

F1

repeat 2 weeks

between 6 and 7

G1

repeat weekly

above 7

X1

intrauterine transfusion

23-27

below 1

A

repeat 4 weeks, deliver at term

between 1 and 2

B1

repeat 4 weeks

between 2 and 4

C1

repeat 3 weeks

between 4 and 5

D1

repeat 1-2 weeks

between 5 and 6

F1

repeat 2 weeks

between 6 and 7

G1

repeat weekly

above 7

X1