### Description

Queenan et al simplified the interpretation of the change in optical density of amniotic fluid at 450 nm (delta OD 450). This can guide the management of a pregnant Rh negative woman with a potentially affected fetus. The authors are from Georgetown University Medical Center in Washington, DC.

Differences from earlier approaches:

(1) covers pregnancies from 14 to 40 weeks (not just 27 to 40 weeks)

(2) delta OD 450 is plotted as a linear variable (not LOG10)

(3) the decision lines are curves rather than straight

There are 4 zones separated by 3 lines.

Zone

Limits

intrauterine death risk

above Line A

affected

between Line A and Line B

indeterminate

between Line B and Line C

unaffected

below Line C

week

Line A

Line B

Line C

14

0.1500

0.1050

0.0520

15

0.1120

0.0580

16

0.1183

0.0650

17

0.1222

0.0700

18

0.1800

0.1240

0.0725

19

0.1800

0.1240

0.0750

20

0.1800

0.1230

0.0750

21

0.1800

0.1210

0.0750

22

0.1800

0.1166

0.0730

23

0.1750

0.1116

0.0710

24

0.1070

0.0680

25

0.1000

0.0640

26

0.0940

0.0600

27

0.0850

0.0540

28

0.0790

0.0500

29

0.1410

0.0717

0.0430

30

0.0628

0.0390

31

0.1310

0.0550

0.0340

32

0.0478

0.0289

33

0.0417

0.0233

34

0.0345

0.0195

35

0.0280

0.0155

36

0.0230

0.0120

37

0.0195

0.0089

38

0.0150

0.0067

39

0.0128

0.0060

40

0.0800

0.0100

0.0056

extracted from Figure 5, page 1374

Line

Weeks

delta OD 450 =

A

14-18

= (0.0075 * (weeks gestation)) + 0.045

A

18-22

= 0.18

A

22-40

= (-0.005562 * (weeks gestation)) + 0.30269

B

14-22

= (-0.000823 * ((weeks gestation)^2)) + (0.03102 * (weeks gestation)) - 0.1679

B

22-40

= (0.00002 * ((weeks gestation)^3)) - (0.001758 * ((weeks gestation)^2)) + (0.043859 * (weeks gestation)) - 0.21

C

14-22

= (-0.000654 * ((weeks gestation)^2)) + (0.026199 * (weeks gestation)) - 0.187045

C

22-40

= (0.0000178 * ((weeks gestation)^3)) - (0.001585 * ((weeks gestation)^2)) + (0.04168 * (weeks gestation)) - 0.26628