Constitutional birth weight determinants in customized birth weight centiles : a systematic review

Objective: Fetal growth restriction (FGR) has a strong negative influence on pregnancy outcome, and identifying this is of great importance in antenatal care. Serial measurement of fundal height is widely used as a screening tool to detect FGR pregnancies, despite lacking evidence of effectiveness in preventing perinatal deaths. One potential avenue of screening is customized growth centiles, adjusted for constitutional factors known to influence birth weight, and thus potentially improving the separation between the constitutionally small vs. the pathologically small baby. The aim of this literature review was to identify the current evidence for the development and use of such customized centiles for screening purposes. Methods: Literature searches were conducted through PubMed, EMBASE, Medline and the Cochrane Databases in English literature after 1990. First, we searched for papers on what potentially constitutional factors affect birth weight. Second, what models had previously been developed for customized centiles. We then explored in depth the characteristics of potentially constitutional factors identified. Finally we searched for evidence of effectiveness screening with customized centiles to prevent adverse pregnancy outcomes. Results and discussion: On the basis of articles found, we have isolated eleven factors being subject of a thorough analysis to decide whether or not to include them in future customized centiles. The factors are: Fetal sex, gestational age, mother and father’s height & weight, parent’s/siblings’ birth weight, parity, maternal age, maternal weight gain during pregnancy, smoking and ethnicity. Conclusion: The following factors should be included in the development of customized birth weight and fetal growth centiles: Fetal sex, gestational age, maternal height and weight, the latter two after excluding the pathology of the extremes. Further, we have found that the effectiveness of customized centiles is promising, however still uncertain and randomized controlled trials are needed to assess their true evidence