The Danish newborn standard and the International Fetal and Newborn Growth Consortium for the 21st Century newborn standard: a nationwide register-based cohort study

Low birthweight: Definition, screening and prediction

“…We employed quantile regression to obtain the BW curves without parametric distribution assumptions. 144,145 In detail, a non-parametric quantile regression within a locally polynomial framework models the relation between GA and BW for both the Danish Population and the Danish Standard cohort. The quantile regressions are fitted as univariate models increasing the comparability to the Intergrowth-21 st standard curves.…”

“…Partially linear fitting between adjacent gestational weeks and piece-wise cubic polynomials with 3-5 knots permit feasible smooth curves. 144,146 This method is robust for the 3% and 97% quantiles, especially in the register data. The Intergrowth-21 st standard BW curve is restricted to GA 33 weeks as the lower limit due to their limit set at minimum 50 observations.…”

“…If there is any occupational risk, sick leave will be recommended. 144 Therefore, the expectation is that potential risk is minized or not present at all for Danish pregnant women in a way that complicates pregnancy above the allowed limit.…”

“…All data handling was done within the environment of Statistics Denmark in an anonymous set-up, where individuals cannot be identified, but it enables linkage between different registries and databases on the individual level. 144…”