The ELGAN (Extremely Low Gestational Age Newborns) Study was designed to identify characteristics and exposures that increase the risk of structural and functional neurologic disorders in ELGANs. From 2002 to 2004, women who delivered before 28 weeks gestation at 14 participating institutions in 11 cities in 5 states were asked to enroll in the study. The enrollment and consent processes were approved by the individual institutional review boards.
Mothers were approached for consent either upon antenatal admission or shortly after delivery, depending on clinical circumstances and institutional preference. One thousand two hundred and forty-nine mothers of 1,506 infants consented. Approximately 260 women were either missed or did not consent to participate. We excluded an additional 71 children because they were not eligible for SNAP-II scoring or did not have all the components for calculating SNAP-II [10
], and an additional 36 infants who did not have a single protocol ultrasound scan were also excluded (table ). The remaining 1,399 inborn infants constituted the sample for this study.
After excluding all deaths, 1,149 infants were eligible for a neurodevelopmental assessment at approximately 24 months post-term equivalent. Not all children evaluated had every component of the assessment protocol. All children who had each assessment were included in the sample for that assessment. Thus, the denominator varies from 964 for head circumference outcomes to 1,042 for the Modified-Checklist for Autism in Toddlers (M-CHAT).
Data were collected by research nurses trained specifically for the ELGAN study. The gestational age estimates were based on a hierarchy of the quality of available information. Most desirable were estimates based on the dates of embryo retrieval or intrauterine insemination or fetal ultrasound before the 14th week (62%). When these were not available, reliance was placed sequentially on a fetal ultrasound at 14 or more weeks (29%), last menstrual period (LMP) without fetal ultrasound (7%) and gestational age recorded in the log of the neonatal ICU (1%).
We collected all the physiology, laboratory and therapy data for the first 12 h needed to calculate a SNAP-II score [10
]. SNAP-II includes points for the lowest mean blood pressure, lowest temperature, lowest pH, respiratory dysfunction (the lowest of PaO2
ratios at 3 points), low urine output and seizures. In addition to these, SNAPPE-II includes points for low birth weight, low 5-minute Apgar score and being small for gestational age. Moribund infants were excluded from SNAP data collection.
We arbitrarily selected a SNAP-II value of 30 or more as high, which identified 28% of our sample, and a SNAPPE-II above a cut-off of 45, which was the score for 33% of the newborns. We also identified cut-offs for each week of gestational age that defined the top quartile and top decile.
The Vermont Oxford Network (VON) SNAP Pilot Project provided the median and standard deviation of SNAP-II and SNAPPE-II for each week of gestation [4
]. This allowed us to create a Z score SNAP-II and SNAPPE-II Z score for each newborn in our study.
The SNAP-II Z score is the difference between the observed SNAP-II and the mean SNAP-II for the same gestational age in the VON sample divided by the standard deviation of the SNAP-II at that gestational age. Because they incorporate the standard deviation, Z scores provide information about SNAP-II variability at each gestational age. They are expressed as units of standard deviations from the gestational age-specific mean and follow a Gaussian distribution with a mean of 0 and variance of 1.
Ultrasound Protocol Scans
Routine scans were performed by technicians at all of the hospitals using digitized high-frequency transducers (7.5 and 10 MHz). Ultrasound studies always included the 6 standard quasi-coronal views and 5 sagittal views using the anterior fontanel as the sonographic window [11
The 3 sets of protocol scans were defined by the postnatal day on which they were obtained. Protocol 1 scans were obtained between the 1st and 4th day (n = 1,075); protocol 2 scans were obtained between the 5th and 14th day (n = 1,247) and protocol 3 scans were obtained between the 15th day and the 40th week (n = 1,215).
After creation of a manual and data collection form, observer variability minimization efforts included conference calls discussing aspects of images prone to different interpretations [12
]. Templates of multiple levels of ventriculomegaly were included in the manual.
All ultrasound scans were read by two independent readers who were not provided clinical information. Each set of scans was 1st read by 1 study sonologist at the institution of the infant's birth. The images, usually as electronic images on a CD imbedded in the software eFilm Workstation™ (Merge Healthcare/Merge eMed, Milwaukee, Wisc., USA), were sent to a sonologist at another ELGAN study institution for a 2nd reading. The eFilm program allowed the 2nd reader to see what the 1st reader saw, and provided options to adjust and enhance the studies similar to the original reader, including the ability to zoom and alter gains.
When the two readers differed in their recognition of intraventricular hemorrhage, moderate/severe ventriculomegaly, echodense (hyperechoic) lesion and echolucent (hypoechoic) lesion, the films were sent to a 3rd (tie-breaking) reader who did not know what the first 2 readers had reported.
24-Month Developmental Assessment
Families were invited to bring their child for a developmental assessment close to the time when s/he would have a corrected age of 24 months. Fully 91% of children had this developmental assessment, which included a neurological examination and the Bayley Scales of Infant Development, 2nd Edition [13
]. Of these children, 77% had their exam within the range of 23.5–27.9 months. All Bayley Scales assessments were age-adjusted as appropriate.
The parent or caregiver accompanying the child was asked to complete the M-CHAT [14
The head circumference was measured as the largest possible occipital-frontal circumference. Measurements were rounded to the closest 0.1 cm when taken at birth and examined at 24 months (corrected age). All head circumferences are presented as Z scores because newborns were assessed at different gestational ages at birth (23–27 weeks) and at different age-corrected approximations of 24 months (range: 16–44 months corrected age, with 68% assessed at 23–25 months corrected age). Z scores were based on standards in the CDC data sets [15
Neurologic examiners used a manual, a data collection form and an instructional CD designed to minimize examiner variability, and demonstrated acceptably low variability [16
]. The topographic diagnosis of cerebral palsy (CP; quadriparesis, diparesis or hemiparesis) was based on an algorithm created using these same sources of information [17
]. Children allocated to 1 CP diagnosis differed from their peers with the 2 other CP diagnoses in their score on the Gross Motor Functional Classification Scale (GMFCS) [18
], as well as in the frequency of microcephaly, cognitive impairment and M-CHAT positivity. Only 4% of the examiners indicated at the time of the examination that they had knowledge of the child's brain-imaging studies.
In addition to performing the neurological examination, examiners rated children on the GMFCS, separate from the neurological examination.
Bayley Scales of Infant Development, 2nd Edition
Certified examiners administered and scored the Bayley Scales of Infant Development, 2nd Edition [13
]. Before testing, the examiners were told the child's age. After completion of testing, they were told the gestational age so that the unadjusted mental developmental index (MDI) and psychomotor developmental index (PDI) could be obtained. Only 2% of the examiners indicated at the time of the examination that they had more than a limited amount of information about the child.
The child was classified as nontestable if her/his impairments prohibited standardized administration or more than 2 items were judged to be ‘not applicable’. On the basis of their score on scale No. 5 of the Vineland Adaptive Behavior Scales, 26 of 33 children considered nontestable were assigned an MDI equivalent of <70 (n = 23) or 70+ (n = 3). On the basis of the motor scale (No. 4) of the Vineland Adaptive Behavior Scales, 32 of 38 children considered nontestable were assigned a PDI equivalent of <70 (n = 27) or 70+ (n = 5). The 7 (6) children not assigned an MDI (PDI) equivalent had no Vineland score available.
The parent or caregiver accompanying the child was asked to complete the M-CHAT [14
]. A child screened positive if 2 of 6 ‘critical’ items were identified or any 3 of the 23 items. Because vision, hearing and motor limitations might account for some children screening positive for an autism spectrum disorder, we limited 1 set of analyses to children who were not blind in either eye, did not wear a hearing aid or receive services for the hearing impaired, and had a GMFCS <1, indicating they had no difficulty walking.
SNAP-II and SNAPPE-II decline with increasing gestational age (). We considered the possibility that a SNAP-II of 35 at 23 weeks conveys different information than a SNAP-II of 35 at 27 weeks, prompting us to classify newborns by their SNAP scores within gestational age strata. This is the equivalent to creating internal-based Z scores. Because we also wished to use an external standard, we created Z scores based on the VON data.
Fig. 1. Box and whiskers displays of the central tendency and dispersion of SNAP-II in gestational age groups. The central tendency is indicated by the line close to the middle of the box, which is the median, and by the top and bottom of each box, which indicate (more ...)
Each child was classified by 4 dichotomies of SNAP-II (an arbitrary cut-off at 30, the highest quartile for gestational age, the highest decile for gestational age and a Z score >1), and the equivalent 4 dichotomies of SNAPPE-II (with an arbitrary cut-off at 45). Doing so allowed us to evaluate which derivative of SNAP-II conveyed the most discriminating information.
We evaluated the following generalized null hypotheses:
1 High SNAP-II or SNAPPE-II scores do not predict ultrasound lesions of the brain;
2 High SNAP-II or SNAPPE-II scores do not predict neurodevelopmental dysfunctions;
3 High SNAP-II or SNAPPE-II scores do not predict a head circumference >2 standard deviations below the expected mean;
4 Distributions of SNAP-II and SNAPPE-II do not vary appreciably among children with and without ultrasound lesions of the brain.
5 Distributions of SNAP-II and SNAPPE-II do not vary appreciably among children with and without each neurodevelopmental dysfunction at approximately 24-month post-term equivalent.
6 Distributions of SNAP-II and SNAPPE-II do not vary appreciably among children with and without a head circumference >2 standard deviations below the expected mean at approximately 24-month post-term equivalent.
We evaluated the first 3 hypotheses with logistic regression models that adjusted for gestational age by both week of gestation and groups of weeks [19
]. Each adjustment provided almost identical results. We prefer the groups of weeks because it minimizes the degrees of freedom. To account for the possibility that infants born at a particular hospital are more like each other than like infants born at other hospitals, a hospital cluster term was included in all models [24