Portuguese versus Fenton Curve: Which one better explains maternal and neonatal outcomes in Portuguese women with gestational diabetes?

Background And Aims: Growth charts are commonly used to identify foetal growth alterations, playing an important role as extreme growth centiles correlate with worse foetal and neonatal outcomes. This study aim was to compare birthweight classification (small for gestational age (SGA), adequate for gestational age and large for gestational age (LGA)) from women with gestational diabetes mellitus (GDM) by applying the population-based growth chart (Fenton Curve) and the standard chart customised for our country (Portuguese Curve). Moreover, we compared obstetric and neonatal outcomes according to birthweight classification between these curves.

Methods: A multicentre observational study with prospectively collected data from 19,470 pregnant women diagnosed with GDM (30 Portuguese institutions) was conducted.

Results: The proportion of SGA neonates was higher with Fenton Chart than with Portuguese standard chart (12.7% vs 10.9%) and the prevalence of LGA was higher using the Portuguese Chart (4.1%vs 10.9%). Statistically significant differences in the classifications given by the two curves and for maternal/neonatal outcomes were found. The Area Under the Curve and Akaike Information Criterion pointed out to a better correlation between weight classification of the Portuguese Curves and the majority of expected maternal and neonatal outcomes: gestational hypertension, preeclampsia, hydramnios, vaginal dystocic labour, hyperbilirubinemia, respiratory distress syndrome, trauma from delivery, admission in neonatal intensive care unit, prematurity and neonatal morbidity.

Conclusion: Our study highlights the importance of having a standard birthweight curve specifically designed for each population. Neonates' weight classification carries prognostic implication and misclassification could lead to potential mistreatment or overtreatment.