Patient population
We conducted a retrospective chart review of all neonates with a gestational age of more than 37 weeks and a birth body weight (BW) of more than 2500 g from January 2007 to December 2008 at a medical hospital. The exclusion criteria were a history of birth trauma, cephalohematoma, instrumental delivery, exposure to certain medications (mother or baby), history of gestational diabetes, early onset hyperbilirubinemia (less than 48 hours), pathological neonatal jaundice (including hemolysis, glucose-6-phosphate dehydrogenase deficiency, congenital infections, and congenital hypothyroidism), prenatal asphyxia, major organ anomalies, small for gestational age infants and infants who were exclusively formula fed.
In total, 166 neonates were excluded due to pathological neonatal jaundice (n = 42), early onset hyperbilirubinemia (n = 10), neonatal infections (n = 37), cephalohematoma (n = 7), prenatal asphyxia (n = 3), major organ anomalies (n = 2), and 65 who were discharged home within 2 days after birth. Three hundred and forty-three newborns were enrolled in further analysis. Gestational age was not analyzed, as the gestational age of all infants in the study was greater than 37 weeks, and most infants were around 39 to 40 weeks.
The study was approved by the institution’s Human Subjects Review Committee of Asia University in central Taiwan.
Methods of analysis
The following variables were analyzed: gender, gestational age, birth BW, BW on the first day (24 hours) after birth (day 1), BW on the second day (48 hours) after birth (day 2), BW on the third day (72 hours) after birth (day 3), BWL/percentage on day 2 and day 3, feeding style (exclusively breast fed or mixed feeding), delivery method (normal spontaneous delivery or cesarean section), and total bilirubin level on day 3.
Exclusive breast feeding is the optimal initial feeding style for infants according to the WHO treatment guidelines. However, when there was insufficient breast milk formula was given, and the feeding style was classified as mixed feeding.
Transcutaneous total bilirubin was routinely checked in all infants using a transcutaneous device (BiliChek, Respironics, USA), and total serum bilirubin (TSB) was checked by heel stick for blood sampling (direct spectrophotometric method) when the infants presented with a transcutaneous bilirubin level of more than 15 mg/dL. The infants were divided into two groups: the significant hyperbilirubinemia group (total bilirubin level greater than 15 mg/dL 72 hours after birth) [6, 7], and the non-significant hyperbilirubinemia group (total bilirubin level ≤ 15 mg/dL 72 hours after birth). The infants in the significant hyperbilirubinemia group were admitted for phototherapy. The correlations between BWL percentage within the first 3 days and the total bilirubin level 72 hours after birth were analyzed separately. We further analyzed the correlations between the TSB level and related clinical parameters.
Statistical analysis
All statistical analyses were performed using Yate’s correction of contingency, t-test, Mann–Whitney U test, Spearman’s rank correlation, and receiver operating characteristic (ROC) curves. Because some data did not meet the normal assumption after a normal distribution test of the continuous variables, Spearman’s rank correlation was chosen. The results of the descriptive analyses of the independent variables were reported as percentages and mean ± standard deviation (SD). The differences between the groups were presented as 95% confidence intervals (CIs). Probability levels less than 0.05 were considered to be significant. Interobserver agreements in analyzing the scores of the two scoring systems were calculated by kappa statistics. We also examined the test parameters, including sensitivity, specificity, area under the ROC curve (AUC), positive likelihood ratio (LR+), and negative likelihood ratio (LR–) at the various cutoff values. The AUC, calculated using the trapezoidal rule, was considered as a global measure of the diagnostic value of that parameter. LR+ and LR– were calculated for the best cutoff values. The criterion value indicated the value corresponding to the highest accuracy (minimal false-negative and false-positive results). Statistical analyses were performed using SPSS software (version 15.0; SPSS Inc., Chicago, IL, USA).