Study setting and period
The facility-based unmatched case control study was conducted among lactating mothers in Siraro District, Oromia Regional State, South Ethiopia from April 30 to May 30/2022. The District is located 72 km West of Shashamane town and about 330 km from Addis Ababa, the capital city of Ethiopia. The District has an area of 1312.855 square kilometers and has been experiencing erratic rain-fall and a late start to the autumn rains, which affect the food security situation in the area. At present the District has 1 District hospital, 6 health centers, 32 health posts, 11 private clinics and 4 drug stores [26].
Study population
All lactating mothers who visited Siraro District public health facilities were our source population. All lactating mothers who visited Siraro District public health facilities during the study period were our study population. Cases were defined as lactating mothers who had a BMI < 18.5 kg/m2 during the study period from the selected health facilities where as controls were lactating mothers who had a BMI ≥ 18.5 kg/m2during the study period from the selected health facilities.
Inclusion and exclusion criteria
For cases, all lactating mothers who had a BMI < 18.5 kg/m2 and gave birth before six weeks prior to the study period and were able to give oral consent were included in the study, while for controls, all lactating mothers who had a BMI ≥ 18.5 kg/m2 and gave birth before six weeks prior to the study period and were able to give oral consent were included in the study. Two controls were selected for each underweight mother on the same day as the cases. Non-lactating mothers and those with hearing impairment or physical deformities were excluded from the study.
Sample size determination and sampling technique
Sample size was calculated using Epi-info-7 using the assumption of 95% confidence level, 80% power, control to case ratio of 2:1, age of the mother at first pregnancy was taken from the study conducted in Dangila District, Ethiopia [3] and 10% non-response rate, the final sample size was estimated to be 390 (130 cases and 260 controls) lactating mothers.
There are seven public health facilities that give health service for the peoples living in Siraro District (one District hospital and six health centers). From these facilities, 30% of them (3 health centers) were selected by lottery method. Based on the annual child immunization report from selected facilities, population proportion to sample size allocation was made to each selected health facilities. All lactating mothers who had a child age from 6 weeks to 23 months old who visited health facilities for maternal and child health services were consecutively screened for their nutritional status during entry to the service points. Based on the eligibility criteria, lactating mothers with BMIs of < 18.5 kg/m2 were designated as cases and mothers with BMIs of ≥ 18.5 kg/m2 were designated as controls. As the case was identified, two controls were taken consecutively on the same day as the cases. If more than 2 eligible controls were found at the same time, then two of them were randomly selected.
Data collection tool and procedures
An interviewer-administered structured questionnaire was developed after reviewing relevant related literatures [17, 18, 29, 30]. To ensure consistency, the questionnaire was written in English, translated into the local language (Afaan Oromo), and then translated back into English by language experts. The questionnaire included sections on socio-demographic and economic factors, obstetric factors, environmental factors, and nutritional factors. A battery-powered digital scale and wooden height board were used for the measurement of weight and height, respectively. Four trained BSc nurses were recruited for data collection and one BSc nurse was recruited for supervision based on their previous experience with data collection.
Variable measurement
Weight was measured using calibrated battery-powered digital scale and the reading was taken to the nearest 0.1 kg. Height was measured using height board scale and the respondents were asked to erect upright on barefoot, the reading measurement was taken to the nearest 0.1 cm. Body mass Index was simultaneously computed using WHO BMI Calculator for each respondent. Then, those who had BMI < 18.5 kg/m2 were classified as cases and those who had BMI ≥ 18.5 kg/m2 were classified as controls according to WHO BMI classification.
Independent variables were categorized as follows: age (< 25, 25–32 & > 32 years), residence (urban & rural), marital status (married & live with partner, live alone), occupational status (housewife &others), ethnicity (Oromo, Amhara, Hadya& other), educational status (no formal education, primary & secondary), household head (husband & wife), wealth index (poor, medium & rich), parity (≤ 3, 4–5 & ≥ 6), ANC follow up (yes & no), place of delivery (home &health facility), PNC service (yes &no), birth interval (< 24 months & ≥ 24 months), exclusive breast feeding (yes &no), duration of breast feeding (≥ 2 years& < 2 years), age at first pregnancy (< 18 & ≥ 18 years), nutritional counseling (yes & no), food consumption score (poor & good), dietary diversity score (inadequate & adequate), latrine availability (yes & no), water source (unimproved &improved), waste disposal area (open field, in the garden & pit).
Operational definition
Dietary diversity score
Is the sum of 9 food groups eaten by the mother over the last 24 h prior to interview, serves as a proxy indicator of nutrient adequacy. Nutrient adequacy was classified as inadequate dietary diversity (mean value < 5.74) and adequate dietary diversity (≥ 5.74) based on the 9 food groups recommended by the Food and Agricultural Organization (FAO) [19]. Dietary diversity score measurement is validated in Ethiopian context.
Food consumption score
Is a score calculated using the frequency of consumption of 9 food groups consumed by the mother during the 7 days before the day of interview. Mothers whose food consumption score (FCS) was less than the mean (< 46.5) were considered as poor FCS and those who had FCS of greater than or equal to the mean were categorized as having good FCS (mean > = 46.5). The reliability of FCS question was checked by the Cronbach’s alpha and it was estimated to be 0.647.
Improved water source
Includes piped household water connection inside the users dwelling, public taps or standpipes, tube wells or boreholes, protected dug wells, protected springs and rainwater collection [11].
Improved toilet facility
Includes flush or pour-flush to a piped sewer system, septic tank or pit latrine, ventilated improved pit latrine, pit latrine with slab, and composting toilet [11].
Wealth index
We considered both productive and non-productive assets of the household and twenty two variables were selected and explored for assumptions of principal component analysis (PCA). The assumptions were checked using measure of sampling adequacy and Kaiser–Meyer–Olkin (KMO) was (≥ 0.5), Bartellet’s test of spherecity (p < 0.05) and anti-image correlation (> 0.4). Variables with communalities less than 0.5 and correlations > 0.4 in more than one component were removed after further iteration because of their exhibited complex structure. Nine variables had eigen value greater than 1 and collectively explained the variance in the set of variables were computed for further analysis. Wealth index was divided in to tertiles as poor, medium and rich for the purpose of analysis.
Data quality control
The anthropometric measurements for weight and height were calibrated daily before the commencement of next day’s activities. Data collectors and a supervisor were given training for two days about the objectives of the study, methods of data collection and anthropometric measurements. Pretest was done in FandeEjersa Health center and necessary amendments were made before actual data collection was commenced. The questionnaire was checked daily to ensure completeness and consistency of the data. Reliability of the tool for food consumption and dietary diversity related question was checked using cronbach’salpha and it was found to be 0.647 and 0.72, respectively.
Data processing and analysis
The data were checked manually, coded and entered into Epi-Data version 3.1 and exported to SPSS version 23 for analysis. Outcome variable was dichotomized into 1 = cases and 0 = controls. The descriptive statistics were used to describe the characteristics of lactating mothers. The Chi-square test was used to compare the proportion of cases and controls between selected categorical variables and it was reported along its corresponding p-value. Bivariate logistic regression analysis was run for each explanatory variable and variables with p < 0.25 in bivariate logistic regression analysis were entered in to multivariable logistic regression model to control potential confounding effects. Multicollinearity was checked using variance inflation factor (VIF) and it was less than 10 for all independent variables. The fitness of the model was checked using Hosmer and Lemeshow goodness of fit test and it was fit with P-value of 0.067. In the model, adjusted odds ratio (AOR), along with its corresponding 95% confidence interval (CI) was used to estimate the strength of the association. Statistical significance was declared at p-value < 0.05. Finally, the results were reported using text, table and figures.
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