The Children's Hospital of Philadelphia (CHOP) has reported a nomogram for predicting the risk of retinopathy of prematurity (ROP).
Parameters:
(1) birth weight in grams from 400 to 1800 grams
(2) daily weight gain rate in grams per day, from -40 to 80
(3) gestational age in weeks, with lower limit 23 weeks
The model consists of a nomogram with multiple lines:
(1) a line connecting the line for birth weight to daily weight gain
(2) the intersection of this line with an auxiliary axis this is about midway
(3) a line from the point of intersection in 2 to a line showing the gestational age in weeks
(4) this line in turn intersects a probability line for the risk of ROP
|
Point
|
X value
|
Y value
|
|
birth weight
|
(0.11925 * (birthweight)) - 36.947
|
0
|
|
daily weight gain
|
(0.6 * (weight gain)) + 196.5
|
60
|
|
intersection on auxiliary line
|
(30-(intersection line 1)) / (slope line 1)
|
30
|
|
gestational age
|
see table below
|
123
|
|
intersection on probability line
|
(85.5-(intersection line 2)) / (slope line 2)
|
85.5
|
|
Gestational Age
|
X value
|
|
23 weeks
|
0
|
|
24 or 25 weeks
|
13
|
|
26 or 27 weeks
|
26
|
|
28 weeks
|
39
|
|
>= 29 weeks
|
52
|
|
Line
|
Slope
|
Intersect
|
|
between birth weight and daily weight gain (line 1)
|
(y2-y1) / (x2-x1)
|
y2 - ((slope 1) * x2)
|
|
between gestational age and auxilliary line (line 2)
|
(y2-y1) / (x2-x1)
|
y2 - ((slope 1) * x2)
|
LOG10(probability) = P =
= (3.0754 - (0.058829 * (X value at intersection with probability line))
probability of ROP =
= 10^P
Interpretation:
• A probability of type 1 ROP >= 1.4% (0.014) is considered higher risk and underwent eye exam for ROP.
