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Childhood stunting is a public health concern in many low-and-middle income countries, as it is associated with both short-term and long-term negative effects on child cognitive development, physical health, and schooling outcomes. There is paucity of studies on recovery from stunting among under five children in these countries. Most studies focused on the recovery much later in adolescence. We used longitudinal data from two Nairobi urban settlements to determine the incidence of recovery from stunting and understand the factors associated with post-stunting linear growth among under-five children. A total of 1,816 children were recruited between birth and 23 months and were followed-up until they reached five years. We first looked at the time to recover from stunting using event history analysis and Cox regression. Second, we used height-for-age z-score slope modelling to estimate the change in linear growth among children who were stunted. Finally, we fitted a linear regression model of the variation in HAZ on a second degree fractional polynomials in child’s age to identify the factors associated with post-stunting linear growth. The principal findings are: i) the incidence of recovery from stunting was 45% among stunted under-five children in the two settlements; ii) timely child immunization, age at stunting, mother’s parity and household socioeconomic status are important factors associated with time to recover from stunting within the first five years of life; and iii) child illness status and age at first stunting, mother’s parity and age have a strong influence on child post-stunting linear growth. Access to child health services and increased awareness among health professionals and child caregivers, would be critical in improving child growth outcomes in the study settings. Additionally, specific maternal and reproductive health interventions targeting young mothers in the slums may be needed to reduce adolescent and young mother’s vulnerability and improve their child health outcomes.
We used longitudinal data collected from the Maternal and Child Health (MCH) study implemented by the African Population and Health Research Center (APHRC) in two informal settlements in Nairobi. The MCH study was nested within the Nairobi Urban Health and Demographic Surveillance System (NUHDSS) that APHRC has been running since 2002 in Korogocho and Viwandani informal settlements in Nairobi. In addition to a wide range of demographic events (births, deaths, migration) and socioeconomic information (household amenities, possessions and livelihoods, education, marital status), obtained through the NUHDSS, the MCH study also collected data on maternal health (pregnancy, delivery, antenatal care) as well as on child health (postnatal care, diseases, feeding practices, vaccination and anthropometric measurements). Further information on the NUHDSS can be found in Emina et al. [32] and Fotso et al. [33]. The study recruited cohorts of mother-child pairs that were visited every four months between October 2007 and September 2012. A mother-child pair was recruited if the child was born in the informal settlements and was six months old or younger at the time of recruitment. Each child was followed-up to the age of five years. However, some of them were not observed at all survey rounds because of outmigration or death. Each observed child contributed on average 2.4 years of data and the median number of observations per child was seven. Mothers of at least one living child, and for whom no important information (e.g. child date of birth or mother’s age) was missing or implausible, were included in this study. Table 1 provides summary statistics on linear growth for the study sample at about two years (20–27 months) and five years (56–59 months). We compared all children to those who were stunted at any time during the observation period. The mean height for the total study population at two years (79.43 cm) and five years (101.88 cm) remained below the World Health Organization (WHO) standards for the same periods (respectively 86.57 cm and 108.63 cm). More importantly, the mean height-for-age z-score (HAZ = -2.17) was below the WHO cut-off for stunting (HAZ = -2) at two years mean, reflecting a stunted population at that time. However, at 5 years, the children seemed to be recovering from stunting (mean HAZ = -1.42). The same pattern was observed if we look at only the children who were stunted (HAZ = -2.58 at 2 years; HAZ = -1.75 at 5 years). We first looked at the time to recover from stunting using event history analysis. In this case, the ‘failure event is recovery from stunting which is defined by an increase in the height-for-age z-score (HAZ) between two time points t1 and t2, such that HAZ(t2) ≥ -2. Apart from its simplicity, the main advantage of this definition is that it reflects a dynamic assessment of growth and can be used consistently over the whole growth trajectory as noted by Wit et al [17]. In addition, the method uses all time points available and accounts for multiple failures during the observation period. Using Cox regression analysis, we identified the factors associated with the time to recover from stunting. Second, we used HAZ slope modelling to estimate the change in height-for-age z-score among children who were stunted at any time during the observation period. The difference in HAZ for each stunted child is estimated by fitting a line through the points, starting from the first stunting episode, and using the slope for the individual as the measure of change over time [17]. The approach is suitable for this study as the children were observed at several time points (the median number of observations per child is 7), and accounts for the non-linear individual growth trajectories. Once the difference in HAZ was estimated, we then fitted a linear regression model of ΔHAZ on a second degree fractional polynomials in age of the child at first stunting to identify the factors associated with post-stunting linear growth. Since sex differences among children were already taken into account when computing the HAZ, we did not fit the models separately for boys and girls. Children born from a multiple pregnancy were excluded from the multivariable analyses. Building on the literature on child catch-up growth [14, 15, 34–36], we considered child, maternal and household level factors documented as potential determinants of recovery from stunting. At the child level, we included individual characteristics such as sex, age, birth weight, place of delivery, immunization status (up to date vs. not up to date), and number of illness symptoms reported over the last two weeks preceding each survey round. At the maternal level, we considered covariates including (age, slum of residence, education, ethnicity, marital status and parity at child’s birth). Finally, the household size and socioeconomic status, estimated using principal component analysis (PCA) based on household assets [37], were included among the potential determinants of recovery from stunting. The study was approved by the Kenya Medical Research Institute ethical review board at the time of data collection and by both the Human Research Ethics Committee (Medical) at the University of the Witwatersrand, South Africa for secondary analyses of the data. During the MCH data collection, all interviews were conducted in private places and written informed consent was sought from all participants.
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