This is depicted in Figure 1b, where the red and green dashed curves do not occupy the same birthweights except for a small interval near 1700 g.
Indeed, in the only study that compared absolute birthweight and centile chart in the same population, the association for birthweight below the tenth centile was observed to be stronger than the association with absolute birthweight below 2.9 kg, for this outcome.
The results remained the same after adjusting for birthweight.
Figure 5 shows the 3rd, 10th, 25th, 50th, 75th, 90th and 97th centiles superimposed on the actual birthweights for the same groups.
We used the same data set to estimate birthweight-specific mortality curves for the lower residual and predominant distributions in a contaminated normal model [ 5].
The objective of the study was to investigate the association between pregnancy complications and small for gestational age (SGA) birthweight, comparing SGA based on the customized growth potential with SGA based on the birthweight standard of the same population.
Only one study compared two birthweight standards in the same population.
After adding the two potential mediators (i.e., smoking during pregnancy and prenatal care visit), the associations between the main predictors and birthweight remained largely the same, suggesting no mediation (model 2, Table 4).
Although the combined analysis of the two separate trials cannot be considered equivalent to a single trial enrolling both low birthweight and normal birthweight neonates and randomising them to the same type of treatment at the same time, it seems clear that girls in Guinea-Bissau do not benefit from neonatal vitamin A supplementation.
22 The Peters test was performed where there were ten or more studies included in the meta-analysis (population <10th centile and childhood morbidity and birthweight <2.5 kg for the same outcome).
