Gestational Diabetes Mellitus (GDM) can affect foetal and neonatal growth, with limited evidence on biometry at 12 months. This study aims to explore growth patterns and identify factors influencing foetal, neonatal, and 12-month biometry in GDM-exposed infants. In a single-centre, retrospective study, we followed 76 women for GDM; foetal (abdominal circumference and relative centile) and neonatal (birthweight and relative centile) biometry, as well as data at 12 months (weight, relative centile and ponderal index) were recorded. In foetal age, 84% of children had appropriate growth centiles (Appropriate for Gestational Age, AGA), 3% had a centile <10th (Small for Gestational Age, SGA), and 13% >90th (Large for Gestational Age, LGA). Eighty-four percent of newborns were AGA, 3% were LGA, and 13% were SGA. At 12 months, 70% had appropriate weight, 22% had weight >90th, and 8% had weight <10th. By dividing the sample based on foetal growth centile (SGA vs AGA vs LGA), SGA children regained growth, reaching a higher growth centile at birth and 12 months, compared to AGA and LGA foetuses. LGA foetuses reached an appropriate growth centile both at birth and at 12 months, while AGA foetuses maintained a stable growth pattern. Infants from Assisted Reproductive Technology (ART) had higher foetal growth centiles (72nd vs 57th, p=0.027), correlating with maternal age (r=0.233, p=0.043). Maternal treatment with L-thyroxine led to higher birthweight (3349 g vs 3066 g, p=0.002), while inositol treatment correlated with higher centiles (46th vs 32nd, p=0.035). Neonatal weight correlated with maternal height (r=0.316, p=0.005) and weight gain (r=0.244, p=0.035). At 12 months, ART-born infants maintained a higher ponderal index (2.48 vs 2.25, p=0.039), and caesarean-born infants had higher weight centiles (62.97th vs 47.61st, p=0.026). Factors such as the use of ART, maternal treatments, age, biometry and type of delivery can significantly influence foetal and neonatal growth. Understanding these factors is important for optimally managing pregnancy in women with GDM and ensuring healthy growth of newborns.