During the last 3 months of pregnancy, large amounts of calcium and phosphorus are transferred from the mother to the baby. This helps the baby grow.

A premature infant may not receive the proper amount of calcium and phosphorus needed to form strong bones. While in the womb, fetal activity increases during the last 3 months of pregnancy. This activity is thought to be important for bone development. Most very premature infants have limited physical activity. This may also contribute to weak bones.

Very premature babies lose much more phosphorus in their urine than do babies that are born full-term.

A lack of vitamin D may also lead to osteopenia in infants. Vitamin D helps the body absorb calcium from the intestines and kidneys. If babies do not receive or make enough vitamin D, calcium and phosphorous will not be properly absorbed. A liver problem called cholestasis may also cause problems with vitamin D levels.

Water pills (diuretics) or steroids can also cause low calcium levels.

Most premature infants born before 30 weeks have some degree of osteopenia, but will not have any physical symptoms.

Infants with severe osteopenia may have decreased movement or swelling of an arm or leg due to an unknown fracture.

Osteopenia is harder to diagnose in premature infants than in adults. The most common tests used to diagnose and monitor osteopenia of prematurity include:

• Blood tests to check levels of calcium, phosphorus, and a protein called alkaline phosphatase
• Ultrasound
• X-rays

Therapies that appear to improve bone strength in infants include:

• Calcium and phosphorus supplements, added to breast milk or IV fluids
• Special premature formulas (when breast milk is not available)
• Vitamin D supplementation for babies with liver problems

Fractures will most often heal well on their own with gentle handling and increased dietary intakes of calcium, phosphorus, and vitamin D. There may be an increased risk for fractures throughout the first year of life for very premature infants with this condition.

Studies have suggested that very low birth weight is a significant risk factor for osteoporosis later in adult life. It is yet unknown whether aggressive efforts to treat or prevent osteopenia of prematurity in the hospital after birth can decrease this risk.

Neonatal rickets; Brittle bones - premature infants; Weak bones - premature infants; Osteopenia of prematurity

Abrams SA, Tiosano D. Disorders of calcium, phosphorus, and magnesium metabolism in the neonate. In: Martin RJ, Fanaroff AA, Walsh MC, eds. Fanaroff and Martin's Neonatal-Perinatal Medicine. 11th ed. Philadelphia, PA: Elsevier; 2020:chap 87.

Eitel KB, Koves IH, Ness KD, Salehi P. Disorders of calcium and phosphorus metabolism. In: Gleason CA, Sawyer T, eds. Avery's Diseases of the Newborn. 11th ed. Philadelphia, PA: Elsevier; 2024:chap 83.

Updated by: Neil K. Kaneshiro, MD, MHA, Clinical Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.