It is widely accepted that maternal drug-exposed infants demonstrate excessive early weight loss, but this has not previously been quantified. Among 354 term, substitute methadone-exposed infants, median maximal weight losses were 10.2% and 8.5% for breast- and formula-fed infants, respectively (p=0.003). Weight loss was less in small for gestational age compared to appropriately grown infants (p<0.001). There was no association between maximal weight loss and plasma sodium concentration (p=0.807). Relative to non-drug exposed infants, weight loss was more marked in formula-fed infants, 48% of whom demonstrated weight loss in excess of the 95th centile (compared to 23% of exclusively breastfed infants; p<0.001). Median weight loss nadir was on day 5, excepting those infants exclusively breastfed (day 4). These data suggest that excessive neonatal weight loss among breastfed infants of drug-misusing mothers does not necessarily reflect poorly established lactation and may help to guide management of breast feeding in this population.
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Although excessive postnatal weight loss is often included in the description of neonatal abstinence syndrome (NAS),1 the extent of this has not been quantified. Knowledge of typical weight loss patterns and their relationship (if any) to plasma sodium concentration would guide professionals in their support of feeding for this vulnerable population, an important task given that breast feeding is independently associated with a reduced risk of requiring pharmacological treatment for NAS.2 We present weight loss data from a large group of methadone-exposed infants born in an inner-city maternity hospital.
This was a retrospective cohort study of term infants born to drug-misusing women prescribed substitute methadone and delivered at the Princess Royal Maternity in Glasgow over the 3-year period 1 January 2004 to 31 December 2006.
Mothers and infants were identified on admission to the postnatal ward and/or neonatal unit (NNU) and information extracted from case notes after discharge. Multiple births were excluded. Infants were weighed at birth and daily until discharge. Maternal polydrug misuse (n=297) was defined as use of illicit drugs in addition to substitute methadone, identified by a combination of self-reports and urine toxicology tests during pregnancy and/or immediately after delivery. Blood sampling (either by heel-prick or venepuncture) was undertaken in all infants with weight loss >15%, in the majority of infants with weight loss >12%, and in other infants at the discretion of the medical staff, most commonly in association with plasma calcium and magnesium prior to commencing pharmacological treatment for NAS. Breast feeding was defined as receipt of maternal breast milk for ≥72 h. Exclusively breastfed infants never received infant formula. Data were anonymised prior to analysis. The local research ethics committee approved this study.
Associations between continuous variables were investigated using correlations. Mann–Whitney tests were used for between-group comparisons. All analyses were done using Minitab (v 15) at a significance level of 5%.
A total of 354 singleton term infants were delivered to 354 substitute methadone-prescribed drug-misusing women over the study period. Data were complete for 98.0% of infants and 98.3% of mothers. Demographics are summarised in table 1. Further demographic details and factors related to the development of NAS have already been described.2
Infants were nursed by their mother's bedside unless a specific indication for admission to the NNU was present. Pharmacological treatment for NAS was commenced according to local protocol which included a modified version of the Lipsitz scoring tool.3 Breast feeding was initiated in 105 mother–infant pairs (29.7%) and a further four infants received their own mother's expressed breast milk. One mother was HIV positive and advised against breast feeding, but otherwise breast feeding was actively encouraged. In total, 72 infants (20.3%) received breast milk for at least the first 72 h of life, with 50 of these also receiving supplementary feeds of infant formula. At discharge 34% of supplemented breastfed infants were still breast feeding compared to 100% of those 22 infants exclusively breast fed for the first 72 h (p<0.001).
Weight loss was greater in breast- than formula-fed infants (10.2% vs 8.5% for the population as a whole; p=0.003) and this effect persisted when infants were grouped according to requirement for admission to the NNU and/or treatment of NAS (table 2). Weight loss in excess of the 95th centile, as described by Macdonald et al,4 was exhibited by 23% of non-admitted exclusively breastfed infants and 48% of non-admitted formula-fed infants.
Median day of maximal weight loss was 5 for all subgroups of infants except exclusively breastfed infants, whose weight nadir was on day 4. For infants who were not admitted to the NNU (n=208), median age at discharge was 7 days; this did not differ between breast and formula feeders. Only 3% (n=5) had regained their birth weight by discharge.
For the population as a whole, small for gestational age (SGA) infants (<9th centile) lost less weight than appropriately grown infants (median 7.9% vs 9.3%, p<0.001).
There was no relationship between maternal methadone dose and neonatal weight loss (r=0.116), and no difference in weight loss between infants of mothers who did or did not polydrug misuse (p=0.217).
Fifty-nine infants had plasma sodium measured within 24 h of maximal weight loss. Weight loss among this group ranged from 4.3% to 17.7%; 35.6% of these infants had a weight loss >12%. Sodium concentrations ranged from 132 to 147 mmol/l. No association was found between maximal weight loss and plasma sodium concentration (Pearson correlation 0.032, p=0.807).
Our data confirm the widely held impression of increased neonatal weight loss in maternal drug-exposed infants. This is likely to be the result of poor or incoordinate feeding, rapid gut transit time and increased caloric expenditure secondary to jitteriness, tachypnoea and poor sleep patterns, all recognised signs of opiate withdrawal.3 5
Predictably, breastfed infants lost a greater proportion of birth weight than formula-fed infants. Among relatively healthy babies who were not admitted to the NNU and who did not develop significant NAS, median maximal weight losses were 10.2% and 8.4% for breast- and formula-fed infants, respectively. This compares with 6.6% and 3.5% reported by Macdonald et al for healthy infants born in Glasgow in 2000.4 The difference was most marked for formula-fed infants, almost half of whom exhibited weight loss in excess of the 95th centile compared to less than a quarter of exclusively breastfed infants. This unexpected finding merits further study with a larger group of infants. One possible explanation is greater severity of NAS in formula-fed infants.2
Macdonald's study included only appropriately grown infants, so the inclusion within our cohort of 27.4% SGA infants (who lost less weight as a group compared to appropriately grown infants) will have underestimated differences in weight loss. We chose not to further subdivide our cohort to maintain reasonably sized groups, and to better reflect clinical practice in which weight loss is generally considered regardless of intrauterine growth.
Weight nadir was late (median day 5 compared with 2.7 for the general population4) and commensurate with this, birth weight was regained slowly with only 3% of non-admitted infants regaining birth weight by time of discharge (median day 7). We did not have access to postdischarge weights, but for those infants who attended follow-up at the maternity hospital, weight gain was not generally problematic.
Most neonatologists would recommend measuring plasma electrolytes in infants with weight loss >12%: although we did not find any cases of severe hypernatraemia, these data include too few babies for that practice to be challenged.
Breast feeding protects against the development of severe NAS and should be encouraged2 unless there are clear contra-indications such as maternal HIV positivity. Infants who breast fed exclusively for the first 72 h were more likely to continue breast feeding than those infants given early supplemental infant formula. It must be noted that weight loss was less marked in exclusively breastfed infants; whether this reflects better lactation, better milk transfer or less severe NAS due to greater transfer of maternal drug is not clear.
For a majority of drug-misusing mothers, breast feeding will be a new experience requiring lots of support and encouragement. Regular weighing of infants is important, but results must be interpreted appropriately. Excessive early weight loss and delayed subsequent weight gain in this population do not necessarily indicate poorly established lactation and early introduction of formula supplements may impact adversely upon longer term breast feeding. These data suggest that, with careful supervision, greater tolerance of early weight loss in breastfed infants of methadone-prescribed drug-misusing mothers may be appropriate.
The authors would like to thank the secretarial and medical records staff at Princess Royal Maternity for their assistance in tracking case notes.
Competing interests None.
Ethics approval This study was conducted with the approval of the local ethics committee.
Provenance and peer review Not commissioned; externally peer reviewed.
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