We developed a reference chart for breast‐fed infants between postnatal days 2 and 11. This chart, together with cases of hypernatraemic dehydration obtained from the literature, was used to define an evidence‐based referral rule. As far as we know, this is the first reference chart for RWC and the first evidence‐based investigation of referral rules to detect infants with hypernatraemic dehydration. Our results show that a reference chart for RWC can be helpful to detect infants with hypernatraemic dehydration.
The RWC chart shows that the mean maximal weight loss occurs 3 days after birth and is 6% for a healthy, breast‐fed infant. This is in agreement with several other studies which reported that breast‐fed infants may lose up to 6%45,46,47
of their birth weight during the first week of life. The American Academy of Pediatrics and others also reported that normal weight loss reaches its peak at 3–5 days after birth.50
Livingstone and the American Academy of Pediatrics Work Group on Breastfeeding suggested that a weight loss of greater than 7% of birth weight indicates possible breast feeding problems.19,50
Others suggested that a weight loss of 8% or more warrants further investigation.16,17,18
Most authors reported that many midwives use the rule of thumb that infants may lose up to 10% of birth weight. Our results show that most infants with hypernatraemic dehydration have a weight loss of 10%. However, referral to a hospital of all infants with a weight of loss of >10% would probably lead to many false positive results in the first week of life, assuming that for screening purposes the specificity needs to be sufficiently high. Therefore, we suggest applying the 0.6th centile (−2.5 SDS) as a criterion for referral to a hospital in the first week of life or using a weight loss of >10% after the first week of life. At the hospital, further diagnostic biochemical testing should be carried out. As it takes some time before insufficient breast feeding leads to weight loss, clinical differentiation between normal infants and those with hypernatraemic dehydration is not really possible in the first 2 days after birth. Infants with a weight loss of >10% (or <−2 SDS) in the first week after day 2, should be monitored closely and require more intensive evaluation of breast feeding and possible intervention to correct problems with breast feeding. Furthermore, referral may also be warranted in infants with other clinical symptoms of dehydration even if weight loss is not particularly high. Clinicians should combine RWC values with examination of the infant, knowledge of feeding patterns, and number of wet diapers and frequency and quality of stools. We suggest using the flowchart in fig 3.
Figure 3Flowchart to detect dehydrated infants or infants at risk of dehydration. *Monitor the infant when mild clinical symptoms are present and refer the infant to hospital when severe clinical symptoms are present.
In addition to the 10% weight loss, another rule of thumb among midwives is that infants regain their birth weight by 10–14 days. The chart in this study shows that 50% of infants have regained their birth weight 8 days after birth, which is also consistent with other reports.6,15
This study also shows that even after 11 days, about a third of infants have not yet regained their birth weight. We also expect that at day 14 a high percentage of infants will not have regained their birth weight. Therefore, we assume that this rule will lead to many false positive results. Macdonald et al15
suggested a revised intervention criterion: offer additional breast feeding support to those losing 10% of their birth weight but still consider this as normal and only consider weight loss above 12.5% or failure to regain birth weight by 21 days as being abnormal and requiring medical assessment. We applied the 12.5% weight loss rule to our data with infants from birth to 11 days old and found a sensitivity of 83.1% and a specificity of 99.9%. This rule has a better specificity (+0.5%) at the cost of a lower sensitivity (−2.4%) compared to the −2.5 SDS rule. With the 12.5% weight loss rule, 2.4% of the cases are missed. We think that a decrease in sensitivity of 2.4% is high and we therefore recommend using the proposed flow chart. However, one could consider using the 12.5% weight loss rule at day 3 as the −2.5 SDS line almost reaches 12.5% at day 3.
In our study we used information from cases with hypernatraemic dehydration reported in the literature. We expected that this information is biased towards the more severe cases of hypernatraemic dehydration, since severe cases are more likely to be reported than mild cases. Recently Moritz et al51
found that only 17% of cases of hypernatraemic dehydration had non‐metabolic complications. Therefore, the sensitivity and PPV in this study are likely to be lower for all infants with hypernatraemic dehydration. On the other hand, PPV may also be an underestimate as this value was based on a minimum incidence rate of hypernatraemic dehydration. It would be very interesting in the future to test and possibly optimise our proposed referral rules using new cases with dehydration.
There is evidence that the degree of weight loss in babies born in a particular environment may be associated with the way that environment is managed.52,53
In populations with “baby friendly” care, the prevalence of hypernatraemic dehydration may be lower than in populations with care that is less baby friendly. We assumed that the prevalence of hypernatraemic dehydration is 7.1 per 10
000 breast‐fed infants. Based on this prevalence we calculated the PPV of several referral criteria. Since PPV is dependent on prevalence, in populations with a lower prevalence (perhaps due to baby friendly care) the PPV may be lower, whereas in populations with a higher prevalence the PPV of the same referral criteria will be higher.
We assumed that RWC expressed as a percentage is uncorrelated with birth weight. This means that a heavy child and a light child have the same distribution of RWC. However, this may not be true, as the degree, timing and variability of RWC may be quite different in small infants compared to large infants. We therefore tested the relationship between birth weight and RWC corrected for age using a linear mixed‐effects model (residual variance
864). We found that an infant with a birth weight of 2.5 kg has on average a 1% greater RWC than an infant with a birth weight of 4.5 kg. As this is a relatively small difference for a large difference in birth weight, we decided to use the methodology unconditional on birth weight. The latter approach is also more convenient in practice than, for instance, various RWC curves for different categories of birth weight.
What is already known on this topic?
- Several authors have proposed different rules of thumbs for identifying abnormal relative weight change (RWC).
- It is suggested that many midwives use the rule of thumb that infants may have a weight loss of 10% (=−10% RWC) but should regain their birth weight by 10–14 days.
What this study adds
- As far as we know, we have conducted the first evidence‐based investigation of referral rules for infants with hypernatraemic dehydration and have developed the first reference chart for relative weight change.
In this study, the weights of the infants were obtained in a research setting. The midwife was instructed to weigh the infant routinely. This means that the number of measurements should not depend on the status of the infant. To determine if this is indeed the case, using standard two‐sample t tests we tested the dependence of the number of measurements and the status of the infants by testing the difference in RWC each day between the infants whose weight was being measured for the first time (besides their birth weight) and those who were being reweighed. We refitted the LMS method without the cases which were possibly reweighed because of a high RWC, and found that the difference between the median RWC in the newly constructed growth chart and the reference chart based on all infants was negligible (<
We conclude that the rule of thumb that infants may have a relative weight loss of 10% is excellent after the first week of life. However, in the first week of life this rule will produce too many false positive results. A chart for RWC can be helpful to detect infants with hypernatraemic dehydration.