Meeting the calcium and phosphorus demands of the premature infant represents a challenge for pediatricians from the early days in the neonatal intensive care unit (NICU) and continuing beyond discharge. The problem is a direct result of a shortened gestational period. The fetus acquires two thirds of its calcium and phosphorus stores during the third trimester. Infants born <30 weeks’ gestation are particularly at-risk for calcium and phosphorus abnormalities, including MBDP. Other risk factors include a birth weight <1,500 g, prolonged immobilization, systemic illness, and chronic exposure to medications that negatively impact bone mineralization, such as furosemide (Lasix), steroids, and phenobarbital.

MDBP describes a constellation of abnormalities in premature infants that results in rickets, osteomalacia, and osteoporosis. The etiology of MBDP is a deficiency of calcium and phosphorus. Classic radiographic abnormalities associated with MBDP include fractures, osteopenia as demonstrated by a “washed out” appearance of the bones, and radiographic evidence of rickets with the classic metaphyseal changes. However, a loss of <40% of bone mineralization can occur without the radiographic changes suggestive of MBDP. Early identification of MBDP is better achieved with biochemical markers, including alkaline phosphatase and phosphorus. Classically, the practitioner will see low levels of phosphorus and elevated alkaline phosphatase. However, even with normal biochemical markers and normal radiologic findings, an infant may still be at risk for MBDP.

To prevent the development of MBDP, supplementation of calcium and phosphorus begins almost at the time of birth, initially parentally and then enterally. Babies are generally transitioned from total parental nutrition (TPN) when they are able to tolerate the change. The choice of nutrition for the enterally fed baby requires careful attention. Table 49.1 reviews the
different types of infant formula. Although breast milk has many advantages over other forms of nutrition, breast milk alone provides preterm infants with insufficient calcium and phosphorus for adequate bone mineralization and eventual growth. To circumvent this problem, expressed breast milk is supplemented with human milk fortifiers (HMF) or infants are given preterm formulas to reflect the intrauterine calcium accretion needs of 105 mg/kg/day, taking into consideration variances in absorption and losses. The appropriate duration of feeds with HMF and preterm formulas has not yet been determined, but most babies receive these interventions until they weigh approximately 2 kg or until discharge from the NICU, whichever is first.