Association between perinatal mortality and morbidity and customised and non-customised birthweight centiles in Denmark, Finland, Norway, Wales, and England: comparative, population based, record linkage study
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  • Published on:
    Bird's eye view misses the benefits of customised assessment
    • Jason Gardosi, Professor of Maternal and Perinatal Health Perinatal Institute and University of Warwick
    • Other Contributors:
      • Oliver Hugh, Senior Statistician
      • Emily Butler, Midwifery Programme Manager

    Kilpi and colleagues’ [1] comparative analysis of databases from the UK and several Nordic countries concluded that the benefits of customised vs population based standards for determining SGA are limited when assessing risk of stillbirth and other adverse outcomes.

    Regrettably their approach was unlikely to be able to elucidate the advantages of a customised standard. For each country’s cohort, the authors compared adverse outcomes for the lowest 10% of pregnancies by weight-for-gestation. Because of the strong association between SGA and outcomes such as stillbirth [2], this is where most at-risk pregnancies and adverse outcomes will be found, regardless of the standard used. We illustrated this in a comparative analysis of customised GROW and 3 other fetal weight standards (see table 2 in [3]): the relative risk for stillbirth was essentially the same for each standard, and customisation had little effect. The same would apply to the country cohorts in Kilpi et al [1].

    The fact that customisation adds little at country level has already been shown some time ago in the (not referenced) study from 24 countries [4], which combined population average birthweights with the proportionality equation we had developed for GROW. This approach can be useful in providing country specific charts where more data are not available, and ought to be supported [5]. However when there is more detailed information, the focus ought to be on subgroups of the population fo...

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    Conflict of Interest:
    The authors work for the Perinatal Institute, a not-for-profit social enterprise which provides training and customized growth chart software referred to in this article.