Infant selection: birthweight <= 1,000 grams
Parameters:
(1) gestational age in weeks
(2) abdominal circumference in millimeters
probability of overall survival =
= EXP(-X) / (1 + EXP(-X))
X =
= 20.8384 - (0.5553 * (gestational age in weeks)) - (0.03999 * (abdominal circumference in mm))
probability of survival without severe morbidities =
= EXP(-Y) / (1 + EXP(-Y))
Y =
= 29.8361 - (0.7518 * (gestational age in weeks)) - (0.0415 * (abdominal circumference in mm))
where:
• survival indicates being alive at hospital discharge
• severe neonatal morbidities include high grade retinopathy of prematurity, high grade intraventricular hemorrhage, periventricular leukomalacia, chronic lung disease and deafness
• outcomes could be predicted independent of birthweight
NOTE: The equations given above are given on page 465 as:
probability of overall survival =
= 1 / (1 + (EXP((-1) * (20.8384 + (0.5553 * (gestational age)) + (0.03999 * (abdominal circumference in mm))))))
probability of survival without severe morbidities =
= 1 / (1 + (EXP((-1) * (29.8361 + (0.7518 * (gestational age)) + (0.0415 * (abdominal circumference in mm))))))
When these equations are used, the results do not resemble the data shown in Figures 3 and 4 on page 466.
