TABLE 1.
Clinical Variables Used at Different Time Points for Model Development and Their Definitions
| Variable | Definitions of Clinical Variables |
|---|---|
| Variables evaluated for time point of birth | |
| Birth weight | Birth weight in grams |
| Gestational age | Gestational age in completed weeks by best obstetric estimate |
| SGA | Small for gestational age (below the 10th percentile). This is determined by the combination of gender, gestational age, and birth weight. |
| Male gender | Male gender |
| Multiple gestation | Multiple gestation (twins, triplets, or greater) |
| Black race | Black, not Hispanic, as reported on obstetric records |
| Antenatal steroids | Administration of antenatal steroids to accelerate pulmonary maturity |
| Tocolytics | Tocolytics administered to mother before delivery |
| Antibiotics | Antibiotics administered to mother before delivery |
| Antepartum hemorrhage | Antepartum hemorrhage (placenta previa, abruption, or threatened abortion) with vaginal bleeding or retroplacental clot, other than bloody show, after 20 wk of pregnancy |
| PIH | Hypertension/preeclampsia/eclampsia, as reported on obstetric records |
| Maternal insurance | Maternal medical insurance: private |
| Maternal education | Maternal educational level: high school or greater |
| Outborn | Outborn status |
| Cesarean delivery | Cesarean delivery (compared with those with vaginal vertex or breech) |
| Surfactant | Administration of surfactant to infant |
| 1 min Apgar (median; 25–75th) | Apgar score at 1 min |
| 5 min Apgar (median; 25–75th) | Apgar score at 5 min |
| Delivery room: intubation | Intubation in delivery room |
| Delivery room: chest compression | Chest compressions in delivery room |
| Variables evaluated at time point of 7 day (in addition to those evaluated at earlier time points) | |
| Days on IMV (to day 7) | Days on conventional ventilator in first postnatal week |
| Days on HFV (to day 7) | Days on high-frequency ventilator in first postnatal week |
| Days on CPAP (to day 7) | Days on CPAP as the highest level of respiratory support in first postnatal week |
| Highest Fio2 on day 7 | Highest Fio2 on the highest level of respiratory support on the seventh postnatal day |
| Surfactant doses | Doses of surfactant received |
| IVH grade | IVH Grade11 diagnosed by cranial ultrasound (assumption made that highest grade of IVH occurs by day 7) |
| Received antibiotics for >5 d | Received antibiotics for >5 d |
| Variables evaluated at time point of 28 d (in addition to those evaluated at earlier time points) | |
| Days on IMV (to day 28) | Days on conventional ventilator in first 28 d if not also on HFV on the same day |
| Days on HFV (to day 28) | Days on high-frequency ventilator in first 28 d |
| Days on CPAP (to day 28) | Days on CPAP in first 28 d |
| Highest Fio2 on day 28 | Highest Fio2 on 28th postnatal day |
| PVL | Periventricular leukomalacia |
| Late onset sepsis | Late onset blood culture-positive infection |
| Episodes of late-onset culture-negative clinical infection | Number of episodes of late-onset blood culture-negative clinical infection treated with antibiotics for 5 or more days |
| Days of parenteral feeding (to day 28) | Number of days on total parenteral nutrition in first 28 d |
| Proven NEC | Stage II or III (Bell staging) necrotizing enterocolitis |
| Spontaneous GI perforation | Spontaneous gastrointestinal perforation |
| PDA | Patent ductus arteriosus |
| PDA requiring treatment | PDA that was managed with medication or surgery |
| Variables evaluated at time point of 36 wk PMA (in addition to those evaluated at earlier time points) | |
| BPD: on ventilator or CPAP at 36 wk (%) | Bronchopulmonary dysplasia, on ventilator or CPAP at 36 wk PMA |
| BPD: on supplemental O2 but not ventilation or CPAP | Bronchopulmonary dysplasia, on supplemental oxygen at 36 wk PMA |
| Days on CV (to 36 wk) | Days on conventional ventilator until 36 wk PMA |
| Days on HFV (to 36 wk) | Days on high-frequency ventilator until 36 wk PMA |
| Days on CPAP (to 36 wk) | Days on CPAP until 36 w PMA |
| Highest Fio2 at 36 wk | Highest Fio2 on highest respiratory support at 36 wk PMA time point |
| U/S: vent. size enlarged (day 28 to 36 wk) | Enlargement of cerebral ventricles on cranial ultrasound closest to 36 wk |
| U/S: PVL or porencephalic cyst (day 28 to 36 wk) | Periventricular leukomalacia or porencephalic cyst on cranial ultrasound closest to 36 wk |
| Hearing abnormality | Abnormal hearing screen before discharge |
| ROP: any stage | Retinopathy of prematurity: any stage identified before discharge |
| ROP: stage 3 or plus disease | Retinopathy of prematurity: stage 3 or plus disease identified before discharge |
| Steroids for BPD | Corticosteroid administration for BPD |
IMV, intermittent mandatory ventilation; PIH, pregnancy-induced hypertension.