Objective: The validity of the rule of thumb that infants may have a weight loss of 10% in the first days after birth is unknown. We assessed the validity of this and other rules to detect breast-fed infants with hypernatraemic dehydration.
Design: A reference chart for relative weight change was constructed by the LMS method. The reference group was obtained by a retrospective cohort study.
Participants: 1544 healthy, exclusively breast-fed infants with 3075 weight measurements born in the Netherlands and 83 cases of breast-fed infants with hypernatraemic dehydration obtained from literature.
Results: The rule of thumb had a sensitivity of 90.4%, a specificity of 98.3% and a positive predictive value of 3.7%. Referring infants if their weight change is below −2.5 SDS (0.6th centile) in the reference chart in the first week of life and using the rule of thumb in the second week had a sensitivity of 85.5%, a specificity of 99.4% and a positive predictive value of 9.2%.
Conclusions: The rule of thumb is likely to produce too many false positive results, assuming that for screening purposes the specificity needs to be high. A chart for relative weight change can be helpful to detect infants with hypernatraemic dehydration.
- PPV, positive predictive value
- RWC, relative weight change
- SDS, standard deviation score
- breast feeding
- weight loss
- growth monitoring
- hypernatraemic dehydration
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Published Online First 31 July 2006
Competing interests: None declared.