Early Onset Acceleration of Fetal Growth in Gestational Diabetes Mellitus: Deciding About When and Whom to Screen for Preventing Fetal Macrosomia

The precise time into pregnancy at which women are screened for gestational diabetes mellitus (GDM) is crucial for determining the benefits of diagnosis. However, this issue remains a source of intense debate among guidance authorities and there is no consensus about when and whom to screen. Since 2010, the IADPSG recommends universal screening with 75g OGTT at 24–28 weeks’ gestation (WG), due to evidence of a positive linear correlation between maternal blood glucose levels around 28 WG and risk of fetal macrosomia. Nonetheless, emerging evidence indicates that initial acceleration of fetal growth (FG) related to GDM, predicting fetal macrosomia, is already underway at 20 WG, thereby suggesting that screening strategies for GDM earlier than the recommended 24–28 WG should be reconsidered (1). By exploiting the routine 19–21 WG obstetrical assessment of FG (anomaly scan), along with the risk stratification system endorsed by the Italian NHS, which offers, in addition to the usual GDM screening test at 24–28 WG, an early 75g OGTT at 16–18 WG to women who are classified as at high risk (HR) for GDM (i.e. previous GDM, pre-gravid obesity, or FPG at first prenatal visit between 5.6–6.9 mmol/L), we aimed to verify whether an early onset acceleration of FG related to GDM would be observed in our pregnant population, and if reversion could occur with current screening recommendations. For this, 769 consecutive women in singleton pregnancies, subjected to both anomaly scan and GDM screening, were retrospectively enrolled at our Institution between Jan 2018-Feb 2020. At a mean time of 20.8 WG, the percentiles of estimated fetal weight (EFW) and abdominal circumference (AC) were significantly higher in women who tested positive for GDM at late screening than in women with normal glucose tolerance (NGT). However, while no differences in the birthweight (BW) percentiles of neonates born to non-HR women diagnosed with GDM at 24–28 WG, with respect to NGT women were observed (p=0.416), neonates born to HR women diagnosed with GDM at 24–28 WG (due to refusal to comply with early screening advices) were significantly heavier (p<0.001). In contrast, both the EFW and AC percentiles, as well as the BW percentiles, were significantly lower in infants born to HR women diagnosed with GDM at 16–18 WG with respect to their late diagnosis counterparts (EFW p=0.001, AC p=0.002, BW p=0.048), and not dissimilar to those of NGT women (EFW p=0.824, AC p=0.873, BW p=0.242). These results were confirmed by regression analysis, while adjusting for maternal confounders. Although an initial acceleration of FG related to GDM can be detected at anomaly scan in non-HR women, reversion occurs with current screening recommendations. Earlier screening strategies should be reserved to HR women, as the acceleration of FG related to GDM in these cases is less responsive to treatment delays. (1) Ref: Li et al. Lancet Diabetes Endocrinol. 2020;8(4):292–300.