Prevalence of Metabolic Bone Disease Among Preterm Infants Using Biochemical Markers at 6 Weeks Post Natal Age at Kenyatta National Hospital

Abstract

Background Over the past 20 years, there has been an increase in the survival of infants born prematurely as a result of better newborn care and facilities. Preterms are at increased risk of various problems including metabolic bone disease. Metabolic bone disease (MBD) of prematurity has been defined as a decrease in the bone mineral content relative to the expected level of mineralization for a fetus or infant of a similar size or gestational age plus biochemical and/or radiographic (1). Preterm neonates are predisposed to MBD of prematurity as they fail to accumulate the essential minerals, namely calcium and phosphorus, required for bone growth that are transferred from the mother to fetus in the last trimester. Children who develop MBD are at risk of poor growth and weight gain, prolonged need for ventilation and as a consequence delayed hospital discharge and risk of rickets of prematurity later on in life. MBD may go undetected as significant demineralization has to occur before it is clinically evident. Screening for MBD is therefore essential early in the course of disease and can be done by assessing bone biochemical markers such as alkaline phosphatase, serum calcium and phosphorus levels. Study Objective To determine the prevalence of metabolic bone disease of prematurity, using biochemical markers, at 6 weeks post-natal age at Kenyatta National Hospital. Methodology This was a cross sectional study conducted at Kenyatta National Hospital, newborn unit and outpatient department. Preterm neonates between 28 weeks and 34 weeks gestation and a birth weight between 1,000 g and 2,000 g, feeding on mother’s own milk, were recruited. Anthropometric measurements were taken after birth. The patients were followed up and at 6 weeks of age and their biochemical markers analyzed. These bone biochemical markers included serum Alkaline Phosphatase (ALP), calcium and phosphorus levels. Anthropometric measurements were taken again at 6 weeks post-natal age. Risk factors were retrieved from the patients' files. The risk factors assessed included feeding history, medication history and co- morbid conditions. xii Results Eighty two neonates were screened for MBD at 6 weeks of life with 46.3% being male while 53.7% were female. The mean gestational age and birth weight was 31.5 weeks (SD 1.8) and 1587.3 g (SD 254) respectively. Of the growth parameters at birth, the mean head circumference was 30 cm (SD 1.6) and the mean length was 39.9 cm (SD 2.56). At 6 weeks, the mean weight increment was 15.9g/day (SD 8.9), length was 0.4cm/week (SD 0.2) and head circumference was 0.4cm/week (SD 0.6). The median day for initiation of feeds was day 4 (IQR 3-4) while the median day for reaching full feeds was day 10 (IQR 8-14). There was no association found between neonatal sepsis, neonatal jaundice, necrotizing enterocolitis, respiratory distress, asphyxia and MBD (p>0.05). Of the neonates screened, 49% were found to have hypophosphatemia while 4.8% had hypocalcemia. The prevalence of MBD was found to be 17% (95% C.I 11-28%). Conclusions The prevalence of MBD of preterms was high at 17% in KNH. There was no significant association between feeding practices, medications used and certain co- morbid conditions with MBD. Recommendations Screening of preterms gestational age less and equal to 34 weeks and less than 2000g from 6 weeks post-natal age.