Breastfeeding and lactation research: exploring a tool to measure infant feeding patterns

Initial drafts of the tool were created based on a methodical review of the literature to find definitions used for infant feeding categories and on the authors’ clinical and research experience. It was designed for use by researchers or research assistants who will ask study participants questions and then complete the chart of feeding categories and scores. We attempted to provide flexibility with respect to timing of data collection and to account for quantity of breast milk and mode of feeding in the first six months following birth (i.e., during the typical period of exclusive breastfeeding). To capture breastfeeding patterns over time, we added a scoring system, so multiple time points could be averaged for a single score. The tool does not collect data about the introduction of complementary foods, specifically, the soft, semi-solid, and solid foods introduced around the middle of the first year.

To assess the face and content validity of the initial tool, we consulted clinical and research experts in the field of breastfeeding and lactation to review the draft (see Additional file 1). We asked for feedback about the tool’s content, specifically, whether they believed we captured descriptions of breastfeeding patterns that would be useful for research projects. The revised tool (see Additional file 2) was then pilot tested with research assistants to determine readability, usability, and burden for potential users.

For the third phase, breastfeeding women were recruited then telephoned by research assistants who worked in pairs. Breastfeeding mothers were recruited following the birth of their baby and before discharge from the postpartum unit of a large Canadian hospital that averages 6,200 births per year [6]. Inclusion criteria for the study were women who had given birth to a single, healthy newborn, planned to breastfeed and were able to breastfeed freely, were able to read and write in English or French, were willing and able to maintain a weekly feeding diary for 6 weeks and to answer 6 English telephone questionnaires (twice within 24 hrs × 3 times over 6 months). Nurses asked patients who met the criteria if they would be willing to learn about the study, then the researcher or a research assistant explained the study to interested mothers and obtained a signed consent and a questionnaire of demographic information.

Research assistants (RAs) collected data at 1 month, 3 months, and 5 months following recruitment. One RA was a registered nurse and certified lactation consultant, one RA was a fourth year nursing student who had completed a maternity course, and one RA was a third year nursing student who had not completed a maternity course. The rationale for selection of RAs was to avoid bias due to expertise in the field of maternity and breastfeeding care. The three RAs were randomized into pairs to make the telephone calls, then the two RAs called study participants within 48 hours of each other to administer the tool. After a first call was completed, the first caller would text her partner to inform her that the second call could be made.

To further test validity (i.e., that we were measuring what we intend to measure), we compared mothers’ diaries with the categories RAs recorded. Participants were given a feeding diary with eight boxes to tick each week for six weeks (see Additional file 3). The fourth week of the diary was compared to the 1 month telephone call made by the first caller. Without knowing the category recorded by the RA, the researcher determined a feeding category based on the boxes ticked by the mother. The two categories were then compared for levels of agreement.

Characteristics of mothers and newborns were summarized using descriptive statistics (mean and standard deviation for continuous variables and frequencies and proportions for categorical variables). Agreement between the two callers and agreement between diaries’ and RAs’ classification of feeding categories was assessed using an intraclass correlation coefficient (ICC). For the ICC, we used two-way mixed and absolute agreement options.

While the score using this tool is correctly an ordinal (categorical) score, it has been suggested that kappa does not function as well beyond the 2 by 2 table and it does not take into account the distance between scores on an ordinal scale [7, 8]. Weighted kappa’s can be used for data of this type but a number of authors have identified problems inherent in its use, and Maclure and Willett concluded that “a logical choice of standard weights makes weighted kappa equivalent to the intraclass correlation coefficient” [7, 8]. For these reasons, the data was treated as ordinal-continuous and the intraclass correlation coefficient (ICC) in SPSS 20 was used to calculate the inter-rater reliability as well as agreement between the RA’s rating and the mother’s diary.

While some researchers have based sample size calculations for ICCs on tests of hypotheses, others have argued that it makes more sense to base sample size calculations on attaining a specified level of precision around the ICC [9]. We anticipated there would be high levels of agreement (0.8 or more) between raters and between the tool and criterion (diary). Based on this supposition, assuming an alpha of 0.05 and a desired width of confidence interval of 0.2, we estimated that 55 subjects would be required [10]. In order to account for 30% attrition due to rates of early weaning and loss to follow-up over the 6 month data collection period, 75 subjects were recruited.

The University of Ottawa Research Ethics Board [File Number: H11-11-02] and the Ottawa Hospital Research Ethics Board [Protocol # 20120200-01H] approved the study. The study was conducted in English but all recruitment material was also available in French.

The final tool, labelled FeedCat Tool, is presented in Additional file 4. It contains two parts: 1) questions asked to determine what and how the baby was fed; and 2) a chart to indicate the feeding category for each time point and recall period. The Feedcat Tool used for the data collection (see Additional file 2) included a scoring system because we were trying to capture breastfeeding patterns by assigning a score to the types of feeding and amount of breast milk. The scoring system provided an average of the scores over time, but this number was not useful when we completed our analysis.

The form was designed to be flexible regarding time points and recall periods for data collection. The number of data collection intervals are optional, and each data collection interval should specify time point and recall period (e.g., at 1 month/24 hour recall, at 5 months/7 day recall). Time points should be determined by the research purpose and the research question, as it could be necessary to track patterns over time or at set time points. For example, if the research question is about maternal self-efficacy, then the researcher will probably be collecting data at fixed time points to determine how mothers are feeding at that time. On the other hand, the priority might be how the baby is fed from birth. In that case, the questionnaire would be asked more frequently to ensure accuracy, and it would pick up from where the last questionnaire finished to provide a complete pattern.

Eleven experts were asked for feedback about the tool. All experts had worked with breastfeeding mothers and babies, and eight experts were also researchers with published papers. The nine experts who responded represented Australia, Canada, Sweden, the United Kingdom, and the United States. There were recommendations to clarify language, to simplify the administration, and to reformat the chart. Response to the use of scores was mixed; some liked it, some did not, and others did not comment.

Seventy-five breastfeeding mothers were recruited for the study from the postpartum unit during three weeks in July and August 2012 (see Table 1 for participant characteristics). We did not record how many patients were approached by the nurses, but very few refused after the researcher or a research assistant explained the study. The main reason given for not joining the study was “too busy”.

Ideally, to measure inter-rater reliability, we wanted the calls to be as close together as possible, but several factors made it difficult including availability of the second RA and availability of mother (e.g., if a participant left to shop or go on vacation after the first call or the second RA was in class or at work). We included all calls made within 48 hours of each other, even though the recall for one time point was past 24 hours. The second caller asked if there had been any significant change in the past 24 hours (e.g., separation between mother and baby or the start of supplements) but the majority of participants said no. These responses were verified, as evidenced by the high inter-rater reliability, and showed that mothers were staying consistent from one day to the next.

Thirty-six participants finished two-paired calls at all three time points. Of the possible 225 paired calls (i.e., 75 participants with 3 collection times), 143 two-RA calls were completed within 48 hours, 17 paired calls were removed because they were more than 48 hours apart, and 9 lacked data because the second caller could not reach the participant (see Table 2 for a description of participation).

Initially, the protocol included calling women who had weaned (i.e., stopped all breastfeeding) again at the next data collection time to establish whether or not they had restarted breastfeeding. In reality, this strategy turned out to be stressful for women, and we stopped calling if a woman said she had stopped breastfeeding. In 5 cases, when the first caller learned a woman had weaned her baby and sensed she might be distressed, the second call was not done out of respect for the mother’s feelings.

Inter-rater reliability for classification of feeding categories by the two RAs indicated excellent agreement (see Table 3). The intraclass correlation coefficient (ICC) measuring agreement between the two RAs ranged from 0.90 (95% CI 0.826 to 0.941) to 1.00 (95% CI 0.996 to 0.999) across the various time points. Agreement between the RAs feeding category at 1 month and mothers’ diaries at four weeks was measured as 0.80 (95% CI 0.662, 0.884; see Table 4). An ICC above 0.75 is considered excellent [11].

Table 5 presents the observed prevalence in our sample within each of the infant feeding categories over time. This homogeneous, self-selected group of participants was clustered in four categories with five of the nine categories having either none or only one mother at each of the six data collection intervals. The majority of mothers were exclusively breastfeeding, and the comparison of 24-hour recall with 7-day recall demonstrates uneven patterns of feeding with women moving in and out of categories over time. The higher rate on the 24-hour recall than on the 7-day recall at every data collection interval indicates mothers would use a supplement occasionally over the week. The sample size fluctuated with the data collection intervals, as some mothers who were not reached at one interval may have completed one or two of the other intervals (e.g., RAs might not have reached a mother at 1 month, but she completed the sessions at 3 months and 5 months).