Preterm Infant

Major bibliographic databases were searched: MEDLINE (using PubMed) and CINHAL, by both authors back to year 1987 (given our 25 year limit), with no language restrictions, and foreign articles were translated. The following search terms as medical subject headings and textwords were used: (“Preterm infant” OR “Premature Birth”[Mesh]) OR (“Infant, Premature/classification”[Mesh] OR “Infant, Premature/growth and development”[Mesh] OR “Infant, Premature/statistics and numerical data”[Mesh] OR “Infant, very low birth weight”[Mesh]) AND (percentile OR *centile* OR weeks) AND (weight OR head circumference OR length). Grey literature sites including clinical trial websites and Google were searched in February 2012. Reference lists were reviewed for relevant studies.
All of the found data was reported as completed weeks except for the German Perinatal Statistics, which were reported as actual daily weights [14 (link)]. To combine the datasets, the German data was temporarily converted to completed weeks. A final step converted the meta-analyses to actual age.

To develop the growth monitoring curves that joined the intrauterine meta-analysis data with the WHO Growth Standard (WHOGS) smoothly, the following cubic spline procedure was used to meet two objectives:
a) To maintain integrity with the meta-analysis curves from 22 to 36 weeks. Integrity of the fit was assumed to be agreement within 3% at each week.
b) To ensure fit of the data to the WHO values at 50 weeks, within 0.5%.
Procedure:
1) Cubic splines were used to interpolate smooth values between selected points (22, 25, 28, 32, 34, 36 and 50 weeks). Extra points were manually selected at 40, 43 and 46 weeks in order to produce acceptable fit through the underlying data. The PreM Growth study (Fenton TR, Nasser R, Eliasziw M, Kim JH, Bilan D, Sauve R: Validating the weight gain of preterm infants between the reference growth curve of the fetus and the term infant, The Preterm Infant Multicentre Growth Study. Submitted BMC Ped 2012) conducted to inform the transition between the preterm and WHO data, was used to inform this step. The Prem Growth Study found that preterm infants growth in weight followed approximately a straight line between 37 and 45 weeks, as others have also noted [9 (link)-11 (link)].
2) LMS values (measures of skew, the median, and the standard deviation) [15 (link)] were computed from the interpolated cubic splines at weekly intervals. Cole’s procedures [15 (link)] and an iterative least squares method were used to derive the LMS parameters (L = Box-Cox power, M = median, S = coefficient of variation) from the multicentre meta-analyses for weight, head circumference and length. The LMS splines were smoothed slightly while maintaining data integrity as noted above.
3) The final percentile curves were produced from the smoothed LMS values.
4) A grid similar to the 2003 growth chart was used, but the growth curves were re-scaled along the x-axis from completed weeks to allow clinicians to plot infant growth by actual age in weeks, and a slight modification (scaled to 60 centimeters instead of 65) was made to the y-axis.

A structured survey and semistructured interview script were developed by the research team (eMethods and eFigure in Supplement 1). The interview consisted of the following components:
For the pilot study, we used data on use of prophylactic indomethacin, ibuprofen, and acetaminophen in preterm infants available from existing evidence published in the Cochrane Database of Systematic Reviews.^{13 (link),14 (link),15 (link)} For the formal study, updated evidence from the recent Cochrane review and network meta-analysis by Mitra et al^{16 (link)} was used. Evidence on prophylactic use of hydrocortisone was drawn from a 2019 individual patient data meta-analysis by Shaffer et al.^{17 (link)}

This cross-sectional study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline. Adults born very preterm (gestational age <32 weeks) or families of very preterm infants currently in the neonatal intensive care unit (NICU) or having graduated from the NICU in the last 5 years were included from across Canada and the United Kingdom. The study was approved by the IWK Health Research Ethics Board, and all participants provided electronically signed written informed consent.
The study was planned in 2 phases. Phase 1, a pilot feasibility study, aimed to test our study questionnaire and provided an opportunity to modify any logistic or methodological issues. Phase 2, a formal study of values and preferences, used our pretested interview questionnaire to describe the variability in health-related values and preferences of former preterm infants and families concerning prophylactic use of COX-Is.

Categorical data are expressed as frequencies and percentages. Continuous data are expressed as mean (SD) for parametric data and median (IQR) for nonparametric data. Post hoc exploratory analyses by participant group (parent of preterm infant vs adult born preterm) were conducted using the Mann-Whitney test, z test, χ² test, or Fisher exact test as applicable. Statistical inferences were based on 2-tailed tests with statistical significance set at P < .05. All quantitative analyses were conducted using Minitab software, version 19 (Minitab LLC).