Neonatal hypocalcaemia due to maternal vitamin D deficiency: a preventable and underestimated condition.

Neonatal hypocalcaemia (NH) is a common metabolic disorder, particularly in preterm and high-risk infants. It may be life-threatening, with a broad spectrum of clinical manifestations, although early-onset cases can remain clinically silent.We describe a premature infant with refractory early-onset NH, secondary to severe maternal vitamin D deficiency. Despite an initial asymptomatic presentation, the infant developed persistent biochemical abnormalities requiring supplementation with calcium, magnesium and high-dose vitamin D. Maternal evaluation confirmed marked vitamin D deficiency with secondary hyperparathyroidism, highlighting the direct impact of maternal status on neonatal calcium homeostasis.This case illustrates how neonatal vitamin D levels depend almost entirely on maternal stores during pregnancy, making maternal hypovitaminosis D a key and preventable risk factor for NH. It also emphasises the underestimated prevalence of vitamin D deficiency among pregnant women worldwide, especially in vulnerable populations. Early recognition and intervention are therefore essential to prevent complications in both mother and child.