Discontinuity indices: a tool for epidemiological studies on breastfeeding

The Discontinuity Index (DI), which measures the percentage of infants who were exclusively breastfed (EBF) at the beginning of a given age interval and had abandoned this mode of feeding at its end, and the relative weight of this discontinuation, was introduced and employed in the National Survey on Breast Feeding and Infant Feeding Practices carried out in Cuba in 1990. The aim of this article is to illustrate, through a specific example, the quality of DI as a simple procedure for assessing breastfeeding trends.

The prevalence of EBF in the 14 provinces of Cuba at discharge from the maternity services and at 30, 60, 120, and 180 days of age, was obtained using data from a national sample of 6661 infants (4820 urban and 1791 rural) which were processed by means of a logistic regression model. Cumulative DI were calculated for the intervals 0-30, 0-60, 0-120 and 0-180 days, and partial DI for the terms 30-60, 60-120 and 120-180 days, for each province and for the whole country.

Cumulative DI show the progress of cessation of breastfeeding and are strongly influenced by previous intervals. The Eastern provinces showed the lowest figures at most of the terms. Discontinuation during the first month of life was particularly high in two Western provinces. Partial DI are more specific and allow discrimination of the intervals at which EBF discontinuation is more frequent. The highest values were observed between 4 and 6 months.

Discontinuity indices are useful complements to prevalence rates in epidemiological studies of breastfeeding. The separate analysis of discontinuation in different periods can be highly useful when comparing trends and in the study of the impact of breastfeeding promotion programmes focused on different age intervals.