Introduction

The definition of infant colic which gains most acceptance in extant literature is that of Wessel (1) which describes this syndrome as paroxysms of irritability, agitation or crying, for more than three hours per day on three days per week for at least three weeks, in healthy children. The infant cries inconsolably, generally during the evening, with no identifiable cause and with normal physical examination findings. This problem usually has its onset during the second week of life, intensifies between the fourth and sixth weeks and then gradually eases, disappearing by the third month of life.

Infant colic is a transitory condition, with no risk of mortality and which does not interfere with the child's growth. Nevertheless, in addition to being an extremely stressful situation for the family and the pediatrician, can alter development through a negative reflex within the interaction between the child and its parents and even have emotional after-effects, leading to the appearance of somatic sequelae with the infant (2).

Prospective studies have demonstrated that colic produces feelings of incompetence in parents, discord between partners and increases the risk of domestic violence and abuse (2,3).

Of all types of pre-verbal behavior, an infants crying attracts its parents attention the most. In an attempt to recognize crying patterns under varying circumstances such as hunger, pain and cold and to perfect the definition of colic, much work has been done with recordings, daily observation and spectrum analysis has been done. The ability of mothers to recognize their children's crying patterns has been demonstrated. The information deriving from such maternal perceptions appears to be trustworthy and crying to be the criteria most trustworthy for the diagnosis of colic (4-7).

With respect to the etiology of colic, from the point of view of gastroenterology, gastrointestinal immaturity or allergy, intolerance of cow's milk, malabsorption and gastroesophageal reflux (8,9). Reinforcing the hypothesis that colic could be the result of intolerance of cow's milk, treatments employing Soya milk or hypoallergenic formulae have produced reductions in symptoms (10,11).

Some authors also point to the importance of family relationships. Forsyth et al. (12) cites worries about feeding and low levels of maternal education as factors associated with colic. For other authors colic could be a symptom of a dysfunction of the mother-child relationship and/or of the family ambit (2,13,14). The environment would be characterized by inadequate manipulation due to inexperience, anxiety, depression or anger on the part of the parents. Experiences of clinical symptoms, dissatisfaction with sexual relations during pregnancy and negative experiences during childbirth have also been associated with the occurrence of colic, as have social isolation during gestation and mothers who are insecure at birth (15). Contrastingly, recent work has suggested that colic is a manifestation of normal emotional development, being an insufficient capacity on the part of the infant to regulate the duration of its crying, which is a question of temperament (16,17).

The improvement of the situation through behavior therapies which modify the way mothers conduct themselves in relation to their children (such as how not to make the baby cry, momentum-based or mechanical vibrating devices, ways of holding the child) supports the theory of extrinsic causes of colic (3,5,9,18,19). Notwithstanding, some of these studies were conducted into hilly selected populations which makes generalization difficult.

With the intention of quantifying the magnitude of the problem, in such a way as to provide data which could improve the ability of pediatricians in the identification of parents who have the greatest chances of their children developing colic and in an attempt to prevent other psychosomatic disruptions, a cohort study was performed in Pelotas, RS.

Methods

This cohort study initially identified all children born live in three maternity hospitals within the city (where 99% of births take place) and whose mothers were resident in the urban zone of Pelotas, Rio Grande do Sul, in the period between May and June of 1999. The mothers, during the period immediately post-birth, were invited to respond to a standard, pre-coded, questionnaire. Mothers who were not in the general ward due to pathologies (whether because of the mother or the child) were excluded from the study.

The size of the sample was calculated by estimated the incidence of infant colic at around 30%, a margin of error of 3% and with a confidence level of 95% A further 20% was added for possible losses and thus the size of the sample was 1,100 children.

The following variables were assessed: parents' demographic characteristics (age, type and years of union, reproductive history), a profile of family relationships (type of relationship between the couple and alterations to that during gestation, paternal reaction on being informed of the pregnancy, alterations to the sexual relationship during gestation and how the mother thought about the support of her partner and family). The quality of pre-natal care was evaluated in accordance with Kessner, as modified by Takeda (20), which combines the number of consultations with the point at which pre-natal care began. These criteria considers mother's who attend more than five times with the first consultation being within the first four months as having received sufficient pre-natal care, while mothers who start after the seventh month of pregnancy and attend less than four times have had inadequate pre-natal care with all other mothers classified as intermediate.

Also evaluated were: the sex and weight at birth of the children, intercurrent clinical conditions during the pregnancy in question, any previous maternal experiences with abortion, stillbirth or sick neonates, acceptance of self-image as a pregnant woman, type of birth, the use of any type of induction during labor, expectations and tiredness related to the birth and social class according to the classification proposed by the Associação Brasileira de Institutos de Pesquisa de Mercado which employs a points system with scores for material goods acquired, education, domestic sanitary conditions and number of household servants and based on this score defines five classes (21).

When the children assessed in the perinatal study were three months old a home visit was made and a standard pre-coded questionnaire filled in with information on the child's health. Children were defined as having had colic if their mothers reported that they cried for more than three hours per day, on more than three days in the week and for at least three weeks. Other factors which could be associated with excessive crying and could be confused with colic were checked (otitis media, fractures, urinary infections). This information was requested for each of the children's three months of life. Variables used to evaluate the number of hours of crying were requested only after the variables indicative of the child's health had been elicited. In this way the mothers did not know the object of the study. After the questions relating to feeding, the mother was asked if her child had or had ever had colic, accepting her own perceptions of this.
All interviews were performed by medical students who had been trained on the application and completion of the questionnaire. Due to the intimate nature of some questions only female interviewers who did not know the objective of the study were employed in the maternity units.

The interviewers coded their own questionnaires and later research directors reviewed coding and classification of open questions. Weekly meetings were held with the aim of perfecting the data collection and the receipt of the material. For quality control purposes supervisors repeated 5% of the interviews, chosen at random.

The database was created using Epi-Info 6.0, version 6.02 software. Data was input twice and then compared using VALIDATE in an attempt to limit keystroke errors. The statistical analysis was performed using SPSS 10.0 for Windows, as was the Chi-square for comparison of proportions. In the multivariate analysis, by non-conditional logical regression, variables were introduced according to hierarchy model causality levels. The first level included socioeconomic and demographic variables; the second family relationships and events related to pregnancy; and the third details about the infant's birth and feeding. For each level a regression by retrograde elimination equation was applied, discarding all variables with p > 0.20. Variables remaining in level one were included in the second level equation and variables at this level with p > 0.20 were once again eliminated. This procedure was repeated for the third level. The 0.20 p level was chosen since confusion variables can affect estimates even when their level of significance does not reach 0.05. For reporting of results only variables with a p value less than or equal to 0.05.

Results

Initially 1,195 mothers responded to the first questionnaire and, of these, 1,086 children were visited at three months. Of the 109 (9.1%) children who were not followed up, 28 had died, two had been abandoned by their parents, one had deaf-dumb parents and the others could not be located. There was no difference between the children who were or were not followed up in terms of the mother's age, pre-natal care or type of birth.

Accepting maternal perception on the occurrence of colic, 870 mothers (80.1%) responded that their children, by the third moth of life, had or had already had colic. However, only 177 children (16.3%) had colic according to the crying duration criteria of Wessel.

Table 1 shows the socioeconomic and demographic characteristics of the population studied, and it can be observed that 60% of the children belong to social classes D or E. The parents of one in five children were not living together at the time of birth. With respect to the mothers' education, only 18% of them had completed 11 or more years of study and 59% were illiterate or had studied for less than 3 years.

Table 1 -
Presence of colics, according to the crying time criterion, regarding socioeconomic and demographic variables. Pelotas, 1999

The incidence of colic was independent of the child's sex, birthweight and social class. Attention was drawn to an increased incidence amongst divorced, separated or widowed mothers, although this association was not statistically significant (Table 1).

As regards pre-natal care, a majority of the mothers had received pre-natal care considered adequate. Almost a third of the mothers were having their first child (Table 2). The start of breastfeeding was almost universal, but duration was low with only 62.5% of the children still being breastfed at three months (Table 3).

Table 2 -
Occurrence of colic in infants, according to the crying time criterion, regarding prenatal variables. Pelotas, 1999

Table 3 -
Occurrence of colic in infants, according to the crying time criterion, regarding breastfeeding. Pelotas, 1999

Variables which assessed the relationship of the parents, alterations to sex life and family support during pregnancy did not reveal any association with the incidence of colic during the first three months of life. Equally, for factors such as the quality of pre-natal care, the type of birth, previous experience of abortion or stillbirth no significant differences were found, as shown in Table 2.

Figure 1 shows the final hierarchy model, i.e. those variables which remain in the multivariate analysis model. Surprisingly the chance of colic in children whose mothers had more education was lower. the majority (81.7%) of parents were between 20 e 39 years old and the incidence of colic was inversely related to the age of the father, thus the chance of colic was 0.43 times greater (95% CI 0.20-0.93) among children with fathers over 40 compare with those whose fathers were between 20 and 29 years old.

Figure 1 -
Final hierarchical model for result of infant's colic. Pelotas, 1999

The negative effect on the newborn of earlier illnesses increased, but its confidence interval continued to include unity and as a consequence this association was not statistically significant. The same was observed for births considered traumatic by the mother

Even after adjustments were made for possible confusion factors the chances of colic were 1.86 (95% CI 1.25-2.77) times greater among children who were no longer receiving their mother's milk than among those that were still breastfeeding. Children born by caesarian also demonstrated a greater likelihood of colic (OR 1.55 - 95% CI 1.04-2.32).

Discussion

Infant colic is a very subjective syndrome; there have been many contradictory findings and many studies have had methodological problems, such as, samples which are not representative of the population, varying definitions of colic, as a recent meta-analysis shows (10). As the primary advantage of cohort studies is the possibility of evaluating the incidence and risk factors of a disease and they are not susceptible to reverse causality distortions, this was the chosen delineation. Additionally, follow-up losses were low and so our study is not susceptible to selection distortions, which can happen in this type of study. Finally, we defined the occurrence of colic using the criteria proposed by Wessel (1), which are the criteria for the diagnosis of colic in infants which has gained most acceptance (10,19).

The non-existence of a standardized definition of colic makes it difficult to determine its magnitude. The literature gives figures of between 10 and 20% of healthy, well-fed infants with colic (10,19). The heterogeneous nature of concepts, methodology and types of studies performed reflects this difference in incidence (19). In the state of Rio Grande do Sul, in 1987, 84.3% of pediatricians reported this as a common complaint in their clinical practice using persistent and inconsolable crying as diagnostic criteria (22). In our study the cumulative incidence of colic as reported by the mothers was 80.1%. However, the cumulative incidence established using Wessel's criteria was 16.3%, demonstrating that colic has a considerable magnitude, although not with the frequency with which the population identifies it and contradicting studies which accept maternal perception (4,5,23).

The association between the development of colic and factors such as the age of the mother, the type of union between the parents, order of birth, birth weight and social class did not demonstrate any significant differences, in common with Lucassen's review (19) and contradicting Crowcroft's study (24).

Other work reporting the existence of an association between caesarian births and colic. As the value of the confidence interval lower limit is a low one we cannot completely reject chance as one of the causes of this finding. Labor considered as traumatic by the parents has been described by Rautava (15) as a factor associated with the development of colic, but not all caesarian sections can be described as traumatic and for those mothers who responded that their labor had been worse than they expected the confidence interval still included unity, ruling out this factor as associated with colic.

In contradiction of Rautava's report (15), we did not observe a greater chance of the occurrence with children whose parents reported they had adapted badly to pregnancy, negative changes to sexual relations or diseases during pregnancy.

When analyzing the presence of an association between breastfeeding and the development of colic, reverse causality is an important distorting factor, since the mothers of crying children may stop breastfeeding because they relate the condition to feeding or believe that their milk is insufficient or weak (25-27). In order to prevent this deviation children were considered to be breastfed if they were receiving their mother's milk at the onset of colic. The analysis continued to show significance demonstrating an effective association between premature weaning and the presence of colic. This finding contradicts others (15,24-27) which compared maternal suckling with bottle feeding although in Crowcroft's study (24) the odds ratio found was only 1.09 and, in Recife, a study by Sarinho et al. (26) also showed that children fed exclusively at the maternal breast have a three times less chance of presenting colic when compared with non-breastfed children, but due to the small size of the sample the association was not statistically significant During the 50s, Wessel offered the concept of the problem most widely accepted, but did not identify any correlation with the type of feeding. Nonetheless, this work is from a time when directions on maternal feeding and maternity care were different to current methods.

The association found between stopping breastfeeding and the chances of colic could be the result of allergy to cow's milk or carbohydrate malabsorption which results in the production of gasses such as carbon dioxide and hydrogen and can cause colic. Which means that a more intrinsic character becomes acceptable for the etiology of colic as described recently in Garrison's meta-analysis, and by other authors (3,5,8-10,25).

There was perhaps a need to better evaluate maternal temperament and the care received by the infant as in literature there ere are descriptions of the mothers of children with colic as depressive, tired women with few positive responses to the care of the child and having inadequate maternal help and these characteristics can make breastfeeding more difficult (7,27).

The association between colic and the premature termination of breastfeeding leads us to another idea related to the problem of colic: colic is one of the most common motives for offering tea to infants, as much by family members as by doctors (26-28). It is also known that the introduction of this practice is an important risk factor for prematurely weaned infants and for its practice to be effective the ingestion of large volumes is necessary (10), which could seriously compromise the child's nutrition Teas are also associated with diarrhea. These factors increase the risks or morbidity and mortality in this age group (29). Therefore it is judged important to emphasize the protective role of mothers' milk and the care that should be taken when confirming the mother's diagnosis of colic.