Background: Hypocalcemia is a frequent metabolic abnormality in preterm neonates, largely due to disrupted maternal–fetal calcium transfer and immature endocrine regulation. Serum phosphorus also plays a critical role in calcium homeostasis, and their imbalance can result in serious neonatal complications. Early identification of at-risk infants is essential for timely intervention.

Objectives: To evaluate serum calcium and phosphorus levels in preterm neonates with and without hypocalcemia and to assess associated maternal and neonatal risk factors.

Methods: This prospective observational study was conducted in the Departments of Paediatrics and Biochemistry, Maharishi Vishwamitra Autonomous State Medical College, Ghazipur, Uttar Pradesh, India, from May 2024 to April 2025. A total of 120 preterm neonates admitted to the neonatal unit within the first 72 hours of life were enrolled. Detailed maternal and neonatal histories were recorded, and clinical examination was performed. Serum calcium and phosphorus levels were measured using standard biochemical methods. Neonates were divided into hypocalcemic and normocalcemic groups based on serum calcium levels (<7 mg/dL for preterm infants). Data were analyzed using descriptive statistics and appropriate inferential tests.

Results: Hypocalcemia was present in 38.3% of preterm neonates. The mean serum calcium was significantly lower in the hypocalcemic group (6.5 ± 0.4 mg/dL) compared to the normocalcemic group (8.3 ± 0.5 mg/dL; p<0.001). Serum phosphorus levels were also lower in hypocalcemic neonates (4.2 ± 0.6 mg/dL) than in normocalcemic neonates (5.3 ± 0.7 mg/dL; p<0.01). Low birth weight, gestational age <34 weeks, maternal pre-eclampsia, and exclusive breastfeeding without early supplementation were significantly associated with hypocalcemia (p<0.05). Clinical manifestations included jitteriness (52%), irritability (31%), and seizures (17%).

Conclusion: Hypocalcemia is a common biochemical abnormality in preterm neonates, particularly those with low birth weight and specific maternal risk factors. Routine screening of high-risk neonates, coupled with timely calcium and phosphorus supplementation, is recommended to prevent complications.