Bone mineralization status measured by dual energy radiographic densitometry in preterm infants fed commercial formulas

Metabolic bone disease and bone mineral density in very preterm infants

OBJECTIVES

To evaluate bone mineral density (BMD) in preterm neonates at discharge and identify the optimum cutoff values for serum alkaline phosphatase (ALP) and phosphorus (P) concentrations to diagnose the severity of metabolic bone disease of prematurity.

STUDY DESIGN

A total of 336 preterm neonates (≤ 31 weeks' gestation and birth weight ≤ 1500 g) were prospectively evaluated for BMD before discharge using dual-energy X-ray absorptiometry.

RESULTS

BMD reference values (at ALP ≤ 500 IU/L) were measured in 279 patients. BMD was classified as poor (<10th percentile) at <0.068 g/cm(2), fair (10th-25th percentile) at 0.068-0.081 g/cm(2), good (25th-75th percentile) at 0.081-0.112 g/cm(2), and very good (>75th percentile) at >0.112 g/cm(2). Increased BMD was associated with a higher birth weight, short duration of parenteral nutrition, and the absence of small for gestational age status, patent ductus arteriosus, intraventricular hemorrhage, and other clinical variables. Metabolic bone disease of prematurity was absent (ALP ≤ 500 IU/L) in 279 cases (83.0%), mild (ALP >500 IU/L and P ≥ 4.5 mg/dL) in 46 cases (13.7%), and severe (ALP >500 IU/L and P <4.5 mg/dL) in 11 cases (3.3%).

CONCLUSIONS

A BMD >0.068 g/cm(2) at discharge indicated a 90.3% probability of not developing metabolic bone disease of prematurity. The factors independently associated with increased BMD included higher birth weight, short duration of parenteral nutrition, absence of intraventricular hemorrhage, exclusive feeding of fortified breast milk, and older age at discharge.

Whole body bone mineral content is similar at discharge from the hospital in premature infants receiving fortified breast milk or preterm formula

BACKGROUND

Prematurely born infants, especially those with very low birth weight (<1500 g) are at risk for metabolic bone disease.

OBJECTIVES

The influence of the type of oral feeding regimen and of other potential determinants of whole bone mineral content in prematurely born infants, when they approached full gestation, were evaluated. Previous studies have mainly examined effects at the level of regional bone.

METHODS

34 infants (21 males and 13 females), all born between 25.4 and 33.7 weeks of gestation, were studied before discharge. Whole body bone mineral content measurements were made just before hospital discharge using a commercial densitometer (Hologic QDR 4500, Hologic Inc, Waltham, MA) at a median age of 40 days (range, 10 to 115 days) after birth.

RESULTS

Expressed as a percentage of whole body mass, bone mass ranged between 0.86% and 1.99%, was similar between girls and boys and correlated positively with birth weight SD (r=0.42; P<0.05) and body weight SD (r=0.35; P<0.05). No difference in bone mass percentage was found between the different types of oral feedings (fortified human milk and preterm formula) or medications studied (corticoids and diuretics).

CONCLUSIONS

Whereas prenatal and postnatal weight gain determines the degree of bone mineralization of premature infants, it appears that the type of oral feeding does not affect differently the postnatal bone mineralization of premature infants, when assessed at the moment of discharge.

Nutrient requirements for preterm infant formulas

Achieving appropriate growth and nutrient accretion of preterm and low birth weight (LBW) infants is often difficult during hospitalization because of metabolic and gastrointestinal immaturity and other complicating medical conditions. Advances in the care of preterm-LBW infants, including improved nutrition, have reduced mortality rates for these infants from 9.6 to 6.2% from 1983 to 1997. The Food and Drug Administration (FDA) has responsibility for ensuring the safety and nutritional quality of infant formulas based on current scientific knowledge. Consequently, under FDA contract, an ad hoc Expert Panel was convened by the Life Sciences Research Office of the American Society for Nutritional Sciences to make recommendations for the nutrient content of formulas for preterm-LBW infants based on current scientific knowledge and expert opinion. Recommendations were developed from different criteria than that used for recommendations for term infant formula. To ensure nutrient adequacy, the Panel considered intrauterine accretion rate, organ development, factorial estimates of requirements, nutrient interactions and supplemental feeding studies. Consideration was also given to long-term developmental outcome. Some recommendations were based on current use in domestic preterm formula. Included were recommendations for nutrients not required in formula for term infants such as lactose and arginine. Recommendations, examples, and sample calculations were based on a 1000 g preterm infant consuming 120 kcal/kg and 150 mL/d of an 810 kcal/L formula. A summary of recommendations for energy and 45 nutrient components of enteral formulas for preterm-LBW infants are presented. Recommendations for five nutrient:nutrient ratios are also presented. In addition, critical areas for future research on the nutritional requirements specific for preterm-LBW infants are identified.