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The variation in stool patterns from 1 to 42 months: a population-based observational study
  1. C D Steer,
  2. A M Emond,
  3. J Golding,
  4. B Sandhu
  1. Department of Community Based Medicine, University of Bristol, Bristol, UK
  1. C D Steer, CCAH, University of Bristol, Barley House, Oakfield Grove, Bristol BS8 2BN, UK; Colin.Steer{at}bristol.ac.uk

Abstract

Objective: To document the normal stool patterns of young children.

Design: Prospective population-based longitudinal study.

Setting: Avon Longitudinal Study of Parents and Children (ALSPAC).

Subjects: 12 984 children, whose parents completed questionnaires at 4 weeks, 6, 18, 30 and 42 months on their frequency of bowel movements and the consistency and colour of their stools.

Results: Stool frequency declined from a mean of 3.0 times/day (3rd centile 0.6, 97th centile 5.9) at 4 weeks to 1.3 times/day (0.6, 2.7) at 42 months. Stool consistency was soft in most babies with nearly half passing liquid or curdy stool at 4 weeks. 14% of babies usually passed a hard stool at 4 weeks, rising to 30% at 42 months. Stool colour was commonly yellow at 4 weeks and had changed to brown by 6 months. Black stools were extremely unusual at all ages.

Conclusions: These data on the changes with age in the stool patterns of young children will be useful for clinicians.

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Changes in the frequency, colour and consistency of the stools of infants and young children are often a major source of concern to parents. Diarrhoea may account for up to 20% of general practitioner consultations,1 while children aged 0–4 years may have the highest prevalence of constipation of all age groups under the age of 75.2 However, definitive guidelines on what constitute normal stool patterns are still lacking,3 with parents and health workers often having different perceptions of what is normal.4

Previous studies on stool frequency in young children have documented a declining trend with age, with some children showing a steady decrease over this period, while others show little or no reduction after 6 months (see supplementary table 1 and supplementary references 1–8).

Stools tend to become harder as the child becomes older. The colour of stools also changes with age: babies usually have yellow stools changing to brown in later life (see supplementary table 2 and supplementary references 1, 3, 6, 7, 9–12).

Most previous studies had limitations due to their small size or study design, restricting application to the general population. We have utilised prospective data from a large population-based cohort study, the Avon Longitudinal Study of Parents and Children (ALSPAC), to document the time trends in stool patterns of young children.

METHODS

A total of 14 541 pregnant women enrolled in the ALSPAC study, resulting in 14 062 live births. The study population had social and demographic characteristics similar to the UK general population according to the 1991 census (http://www.bristol.ac.uk/alspac/).

The stool patterns of the children were assessed by questionnaires sent to the mother or main carer at 4 weeks, 6, 18, 30 and 42 months after birth. Response rates ranged from 90% at 4 weeks to 81% at 42 months. At each age, questions were asked about stool frequency and how often stools matched consistency (hard, soft, curdy or liquid) and colour (brown, yellow, green or black) outcomes.

The categorical responses for stool frequency were recoded to 0.1 (“once a week”), 0.5, 1.0, 2.5 and 6.0 (“four or more times a day”) allowing comparisons across time and providing an estimate of average rates. Consistency and colour outcomes were dichotomised using the combined “usually” and “always” responses as the reference category (see supplementary table 3).

The longitudinal data were analysed using multi-level techniques. Weighted regression analyses were used to investigate the effects of time on stool frequency. Logistic regression was used to analyse consistency and colour outcomes. Levene’s test was used to compare variances in stool frequency at different ages. Centiles for frequency were estimated by fitting cumulative normal curves to the categorical responses. To take account of multiple comparisons and to evaluate practical rather than statistical differences, a 0.1% significance level was used. Stata v 8.2 was used in the analyses.

Ethics approval for the study was obtained from the ALSPAC Law and Ethics Committee and the Local Research Ethics Committees.

RESULTS

Data for at least one outcome were available for 12 984 children (55 121 observations for the five questionnaires). Children with complete data across time represented 44–69% of all children depending on the outcome. Supplementary table 3 provides a summary of the stool data unadjusted for varying participation.

Stool frequency

Figure 1 shows the adjusted trends for the stool frequency data. Frequency of stools showed a steady decline from a mean of 3.0 times/day (3rd centile 0.6, 97th centile 5.7) at 4 weeks, 2.0 (0.7, 3.5) at 6 months, 1.8 (0.8, 3.2) at 18 months and 1.5 (0.7, 2.9) at 30 months to 1.3 (0.6, 2.7) by 3½ years. Boys tended to have slightly higher average stool frequency by 0.12 (95% CI 0.09 to 0.14; p<0.001) times/day. The variability in stool frequency reduced with age (p<0.001): at 4 weeks, babies differed markedly (SD 2.00) but by 3½ years children were more similar in their habits (SD 0.72).

Figure 1 Frequency of bowel movements with approximate centiles.

Stool consistency

Figure 2 illustrates the adjusted data for the usual stool consistency with varying age. Stools at 4 weeks were usually soft, liquid or curdy. By the age of 6 months, curdy or liquid stools were uncommon, with most infants passing soft stools. A significant minority usually passed hard stools, for example 13.6% (95% CI 12.9% to 14.3%) at 4 weeks. The frequency increased after 18 months with 29.8% (28.8% to 30.8%) of children reported to usually pass hard stools at 42 months. Only 1.2% (1.1% to 1.4%) of children usually passed liquid stools at 6 months, decreasing to 0.12% (0.07% to 0.16%) by 18 months.

Figure 2 Percentage of children reported to usually pass stools of varying consistencies by age.

Stool colour

Supplementary figure 3 illustrates the adjusted data for stool colour by age. At 4 weeks, the commonest stool colour was yellow. By 6 months the commonest colour was brown, with less than 10% of children usually passing yellow or green stools. Green stools were rarely observed after 18 months. Black stools were uncommon at all ages with no discernible trend with time, although nearly 23% of children were reported to pass the occasional black stool during the study period.

DISCUSSION

This is the first large longitudinal study to describe the stool patterns of young children. Stool frequency decreased with age, from 3.0 times/day at 4 weeks to 1.3 times/day at 42 months. Unlike other smaller studies, stool frequency was found to be higher in boys. These differences were small and varied with age (up to 0.18 times/day or 10% increase). Variability in stool frequency between children decreased with age as has been found in other studies (see supplementary table 1). Part of the variability in early life may be due to differences in feeding patterns: in this study, 41% and 45% of infants were exclusively breast or formula fed, respectively, at 4 weeks. Later variation might be associated with differences in diet due to ethnic origin, although only 4.8% were from a non-white background.

Stools tend to become harder with age: this may be related to dietary changes or changes in gut motility.4 5 Stool consistency often worries parents: up to 15% of parents may have some concerns in the first 2 years,5 but this may rise to over 40% if the baby is exclusively fed formula feeds during the first 2 months.6 In ALSPAC, hard stools were reported in over 25% of babies at 4 weeks. In contrast, some parents may perceive the passing of loose stools after 18 months as abnormal.4 Our data showed that although such stools became uncommon after 6 months, over 20% of children sometimes passed stools of this consistency even at 42 months.

Yellow stools are frequent in early infancy but are unusual after 6 months as brown stools become more common: this is probably related to the introduction of solids. Green stools are occasionally reported in early infancy and have been attributed to use of formulas with high iron content (see supplementary table 2). After 6 months, children only occasionally pass a yellow or green stool. Consistent black stools are rare, although occasional stools of this colour are more common and may be related to intake of iron or other dietary factors.

The main limitation of this study is that stool pattern was assessed by questionnaire, while some other studies have obtained more objective assessments using stool samples. However, the consistency of our results with other studies is reassuring and suggests that the questionnaires have provided reliable data.

This is the largest study to date documenting the frequency, consistency and colour of the stools of young children. The large sample size and the similarity of the ALSPAC cohort to the UK population make these results an important contribution to defining normal stool patterns in young children.

Acknowledgments

We are extremely grateful to all the families who took part, the midwives who helped recruit them and the entire ALSPAC team, which includes interviewers, computer and laboratory technicians, clerical workers, research scientists, volunteers, managers, receptionists and nurses.

REFERENCES

Footnotes

  • ▸ Additional data are published online only at http://adc.bmj.com/content/vol94/issue3

  • This publication is the work of the authors. Colin Steer and Bhupinder Sandhu are guarantors for the contents of this paper.

  • Funding: The UK Medical Research Council, the Wellcome Trust and the University of Bristol provide core support for ALSPAC. This study was funded by the Medical Research Council (Grant RD1589).

  • Competing interests: None.

  • Ethics approval: Ethics approval for the study was obtained from the ALSPAC Law and Ethics Committee and the Local Research Ethics Committees.

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