In June 2023, we commenced a project to review and update the Maternity and Neonatal eHandbook guidelines with a view to completion in 2024. Please be aware that pending this review, some of the current guidelines may be out of date. In the meantime, we recommend that you also refer to more contemporaneous evidence.
Osteopenia is a significant problem for very premature babies, and there is some suggestion that hypophosphataemia prolongs the need for ventilatory support. Some very premature babies have very ‘thin’ bones on their x-rays. Supplementation with vitamin D and phosphate may be required.
Diagnosis of metabolic bone disease
Issues to note about diagnosis:
- Biochemical tests of osteopenia of prematurity are not definitive.
- Serum phosphate: suspicious if < 1.5, likely if < 1.1 mmol/L.
- The alkaline phosphatase (ALP) is more elevated than usual for preterm babies. Levels above 600 or 800 IU/L are quoted. However, the ALP only rises high if there is bone turnover. If the condition is very severe the ALP may not be very high.
- The calcium level may be normal, elevated or even low.
- A bone x-ray will show very poor mineralisation and as the infants grow can show changes of rickets or fractures.
- An abnormal calcium to phosphate (Ca++ : PO4 ratio in the urine. In normal infants it is less than 1.0 (both measured in mmol/L))
Conversion factors
One of the problems with this area is that the USA, and many books, work in mg, while Australia and Europe use mmol/L.
| Ca++ | 1 mmol = 40 mg |
|---|---|
| PO4- | 1 mmol = 31 mg |
| Mg++ | 1 mmol = 24 mg |
Considerations and recommendations for enteral feeding
| FETAL RETENTION RATES PER DAY IN MID TO THIRD TRIMESTER | HUMAN MILK PER 100 ML APPROX | FM85 PER 5G | HM 100 ML + 5G FM85 | FORTIFIED EBM @ 180 ML/KG/D THE BABY GETS ABOUT | RECOMMENDED PER 150 ML/KG/D (PROBABLY NEEDS TO BE AT TOP END) | |
|---|---|---|---|---|---|---|
| Ca | 2.3-3.0 mmol/kg 90-120 mg/kg | 0.75 mmol (30 mg) | 1.3 mmol (51 mg) | 2.0 mmol (81 mg) | 3.6 mmol (146 mg) | 3.0-5.7 mmol (120-230 mg) |
| PO4 | 1.9-2.4 mmol/kg 60-75 mg/kg | 0.5 mmol (15 mg) |
(34 mg) | 1.6 mmol (49 mg) | 2.9 mmol (88 mg) | 1.9-4.5 mmol (60-140 mg) |
| Mg | 0.10-0.14 mmol/kg 2.4-3.4 mg/kg | 0.15 mmol (3.5 mg) | 0.08 mmol (2.0 mg) | 0.23 mmol (5.5 mg) | 0.4 mmol (9.9 mg) | 0.33-0.63 mmol (7.9-15 mg) |
Remember that not all the minerals given are absorbed and retained. Retention rates for enteral nutrition vary but are about 50-60 per cent for calcium, 70-80 per cent for phosphorus and 50 per cent for magnesium.
Premature babies may need supplementation
Premature infants fed with fortified EBM at 150 mL/kg/day, or more, should be getting enough calcium and phosphate. However, they need to be monitored and may still need supplementing.
Fortification of feeds should start as early as possible as soon as they are tolerating 120 mL/kg.
Vitamin D
About 500 IU/day of vitamin D is required. Pentavite provides 405 units per day. Larger doses have no increased benefit.
Extra phosphate supplementation
If a baby needs supplementation, make a solution of phosphate 0.8 mmol/ml by dissolving one tablet of Sandoz phosphate in 20 mL water.
Begin supplementation with 3 mmol/kg/day in three divided doses (1 mmol/kg/dose tds). The dose should then be titrated against the blood phosphate level over the following weeks. Stop phosphate supplements if the serum phosphate is > 1.8 mmol/L.
Monitoring
‘Bone bloods’ should be monitored every two weeks in very premature babies unless they are found to be phosphate depleted, and if supplements are given they should be measured every week.
Length of supplementation
No one really knows how long to go on supplementing with phosphate. However, it is worth considering that the babies are still growing fast up to and beyond ‘term’.
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Version history
First published: June 2017
Review by: June 2020