Study setting and sample

We used the data from the first waves of the Young Lives Study (YLS), which was conducted in the state of Andhra Pradesh in India during 2002. Young Lives is an international longitudinal study investigating the changing nature of childhood poverty. About 12000 children are being followed in four countries: Ethiopia, Peru, Vietnam and India (Andhra Pradesh). Each country has two cohorts: younger cohort and older cohort. The younger cohort consists of about 2000 children born during 2001–2002 and the older cohort consists of about 1000 children born during 1994–1995 to be followed over a period of 15 years [59, 60]. The YLS is conducted every 3/4 years to collect data on a range of indicators related to the growth and development of children. YLS collects information on child welfare outcomes including nutritional status, growth, physical health, cognitive development, social and emotional well-being and educational development [59–61].

A multistage sampling design was adopted in YLS. In the first stage, two districts were selected from each of the three geographic regions (Coastal, Rayalaseema and Telangana) of Andhra Pradesh. In the second stage, 19 (15 from rural areas and 4 from urban areas) sentinel sites (administrative blocks or ‘mandals’) were selected from the six selected districts. In addition, one sentinel site was selected from the urban slums of the Hyderabad city. In the third stage, villages were selected from rural sentinel sites and wards were selected from the urban sites. All the households with 5–21 months old child (born during 2001–2002) or 87–103 months old child (born during 1994–95) in the selected villages and wards were included in YLS. Overall, 2011 households (with 2011 children) in the younger cohort and 1008 households (with 1008 children) in the older cohort were included in the first wave of YLS. (for details of YLS sampling design, see [59, 60, 62]). As the objective of this study is to examine the effects of pregnancy intention, postnatal depressive symptoms and social support on early childhood stunting, we used data from the first wave of the younger cohort (aged 5–21 months) born during 2000–2001.

The study included only those children where the mother was the primary caregiver of that child. Individuals with missing data on any of the variable included in the model were excluded based on the following criteria: if the respondent was not biological mother or mother died, women unsure about their pregnancy intention, information on postnatal depression could not be collected and child height could not be measured. This resulted in a 9 % of the sample being excluded from the analysis. Of the 2011 children, 1833 (91 %) children whose complete information on pregnancy intention, postnatal depression, social support, height for age z-score and other variables was collected were considered for the study.

Outcome variable

The outcome variable of interest is early childhood stunting. Children with height-for-age Z-score (HAZ) below minus two standard deviations (HAZ < -2SD) from the median of the reference population were considered short for their age or stunted. Such children are also considered chronically malnourished [63]. Children with height for age Z-score below -6 or above 6 were excluded from the analysis (biologically implausible value defined by WHO) [1].

Key independent variables

The key variables of interest are: pregnancy intention (intended, unintended), postnatal depressive symptoms (non-cases, cases) and social support (low, medium, high).

The survey collected data on mother’s pregnancy intention of the index child. The survey asked women “At the time you became pregnant with index child, did you want to become pregnant”. If women reported “yes’ then it was coded as intended pregnancy and if the response was “no” i.e, mistimed/unwanted, then it was coded as unintended pregnancy.

The information on maternal postnatal depressive symptoms was collected soon after the birth of index child. The postnatal depressive symptoms were measured using WHO recommended tools of self-reported 20 items (SRQ20) that consists 20 questions and answer of each question were reported in yes/no/don’t know with a reference period of last 30 days [64]. We count the number of ‘yes’ responses to the 20 questions. If there are 8 or more ‘yes’ responses, then it was classified as a case and less than 8 ‘yes’ responses were classified as non case. The cut of score to determine how many ‘yes’ responses constitute a case have been validated against clinical assessment [65, 66].

The information on any kind of economic support, emotional support or assistance was also collected in the survey. The survey asked women, since last 12 months, did they receive any kind of economic help, emotional help or assistance from work related/trade union (yes, no), community association/co-op (yes, no), women’s group (yes, no), political group(yes, no), religious group (yes, no), credit or funeral group (yes, no), sports group (yes, no), family (yes, no), neighbourhood (yes, no), friends (yes, no), community leaders (yes, no), religious leader (yes, no), politicians (yes, no), government official/civil service (yes, no), charitable organization/NGO (yes, no) and other (yes, no). If women received any kind of help from afore-mentioned group or person, then it was coded as ‘1’ and ‘0’ otherwise. Further, help from each group/person added together which ranges from 0 to 16. If a women reported no help or assistance, then it was coded as ‘low’ social support. If the number of supports ranges from 1 to 4, it was considered as ‘medium’ social support and from 5 to 16 were considered as high social support. The details of the description of social support measurement are presented elsewhere [67].

Other variables

A number of other socio-economic, demographic and residence related variables have also been shown to have the significant effect on childhood stunting. Accordingly we included birth size (average and above, below average), preterm birth (full term, 1–2 week earlier, 3 or more week earlier), age of the child (in months), sex of the child (male, female), ever breastfed (no, yes), serious illness (no, yes), mother’s age at birth of child (<18 years, 18–24 years, 25–29 years, > = 30 years), mother’s education (below primary, primary and above), mother’s working status (not working, agricultural work, others), ante-natal check-ups (no ANC, <4 ANC, > = 4ANC), iron folic acid tablets (no IFA, <90 IFA, > = 90 IFA),tetanus injection (<2 TT, > = 2 TT), household head’s education (below primary, primary and above), sex of the household head (male, female), household size, wealth index (poor, middle, rich), drinking water (improved, non-improved), toilet facility (improved, non-improved), income shocks (no, yes), religion (hindu, muslim, others), caste (scheduled tribes, scheduled caste, other backward caste, others) and place of residence (rural, urban).

The survey collected data on respondent’s (mother/caregiver) perception about size of the baby at birth. YLS asked the respondent when child was born he/she was very small, small, average, large or very large? Very small or small size at birth was coded as ‘below average’, and average, large and very large size at birth was coded as ‘average and above average’.

The information on serious illnesses were also collected during the survey. The survey asked mother/caregiver since the birth of child, whether he/she had any serious illnesses or injury when she thought child might be died? (Yes/No/Don’t know).

The wealth index was calculated using wealth score, which are already computed and given in the YLS dataset. The wealth score was generated through a principle component analysis conducted on a set of variables based on household assets (including radio, refrigerator, bicycle, television, motorbike/scooter, car, pump, sewing machine, mobile, phone, landline telephone, fan, almirah, clock, table, chair, sofa, bedsheet and animals), household quality (including wall, roof and floor) and services (including electricity, drinking water, toilet facility). The lowest 33.3 % households were coded as poor, the next 33.3 % as middle and the remaining 33.3 % as rich.

YLS also collected information on main source of drinking water. Children were classified into two categories according to whether household relied on safe or unsafe water supply for their drinking. Households having piped water into dwelling/yard/plot or using public tap/standpipe or using tube well/borehole or protected dug well were considered as using safe drinking water. Other households were categorized as using unsafe drinking water. Information on type of toilet facility used by household was also gathered in YLS. Improved toilet facilities include flush toilet/pit latrine connected to septic tank. Non-improved toilet facilities include public/shared facility, simple latrine, and toilet in health post or forest/field/open place.

Income shock refers to any events or big changes that significantly reduce the economic welfare of household. Income shocks at the household level were accessed by the answer to the following question in the YLS:

Since birth of child, whether the household suffered from natural disaster (yes; no), decrease in food availability (yes; no), livestock died (yes; no), crop failed (yes; no), job loss (yes; no), serious illness/injury (yes; no) and victim of crime (yes; no). If household suffered from any one of afore-mentioned event were coded as ‘1’ otherwise, ‘0’.

Statistical analysis

Bivariate analysis was done to compare early childhood stunting by sample characteristics using cross tabulation. Further, we used logistic regression model (using generalized estimation equations to take into account the cluster nature of sample) to examine the effect of pregnancy intention, postnatal depressive symptoms and social support on stunting among children aged 5–21 months. Firstly, the unadjusted association between key independent variables and outcome variable was estimated, followed by the association adjusted for potential confounding variables. Unadjusted and adjusted odds ratio and 95 % confidence interval were reported. Moreover, to access whether social support mediates the effects of pregnancy intention and postnatal depressive symptoms on childhood stunting, we used recommended procedure [68]. Variables were included into the multivariate model based on previous studies and their association with childhood stunting in bivariate analysis. All the variables were tested for multi-collinearity using variance inflammation factor (VIF) before being included in the regression models. All the statistical computations were done in STATA 13.0.