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Table 1 Primary data sources and coding

From: Experiences of an earthquake during pregnancy, antenatal mental health and infants’ birthweight in Bhaktapur District, Nepal, 2015: a population-based cohort study

Interview time Variables Primary data sources and coding
  birth outcome  
Follow up Birthweight In Nepal, a birth certificate is provided to each mother who has given birth in a medical facility. It records the date and time of the birth and the baby’s birthweight. Women were asked to report the birth weight of their babies from the birth certificate. Women who gave birth at home and did not have a birth certificate but where a skilled person had measured birth weight using a standard scale were also asked to report the weight. Those who did not measure baby birth weight were not able to be included in analyses. The weight in grams was used as a continuous variable to examine an association among covariates. Birth weight was also categorized into two groups: ≥ 2.5 kg deemed to be normal and < 2.5 kg as low birth weight.
  Mediating variable  
Baseline Symptoms of Common Mental Disorders (CMDs) during pregnancy The Edinburgh Postnatal Depression Scale-Nepali version (EPDS-N) comprises 10 items, scored from 0 to 3 with a total score of 0 to 30. This version has been formally validated against Diagnostic and Statistical Manual (DSM) IV diagnostic criteria among women who had recently given birth in Nepal: Sensitivity 68.43%; Specificity 93.80%; Positive Predictive Value 65% and Negative Predictive Value 94.64 [31]. The EPDS total score was used as a continuous variable to examine a mediation effect. We also reported proportions of the scores: < 9, 10 to 12 and ≥ 13 to enable comparison between groups.
  Independent variables  
Baseline Earthquake experiences Study-specific questions adapted from previous studies [9, 20] collecting information about 17 items: where they are living now (1 item); property damage (3 items); impact on daily life including basic needs (6 items); being injured/trapped (2 items); witnessing injury/people trapped/death (4 items), intensity of fear experienced during the earthquake (1 item). Details of these items have reported elsewhere [11]. Each item was scored 0 (not experienced) to 1 (experienced) and summed to create a total score. The score ranged from 0 to 17. The total score was grouped in tertle, and low tertile was labelled as low, and middle and upper tertile labelled as middle/high earthquake experiences.
  Covariates  
Baseline and follow up Length of gestation at birth Date of the baby’s birth and the date of the last menstrual period were recorded to calculate the length of gestation at birth. At baseline, we asked participants about their date of last menstrual period.
In the follow-up interview, date of baby birth was recorded. The last date of menstruation was subtracted from date of baby birth and divided by seven to calculate the total weeks as the length of gestation at birth. We used weeks as a continuous variable to examine an association with other variables.
Baseline Socio-demographic characteristics Study-specific questions adapted from our prior research [39] to ascertain women’s age, highest educational level, employment, consume chewing tobacco/smoking, and alcohol, household economics, family structure, and husband’s education, employment, consumption of chewing tobacco/smoking, and alcohol.
Household economics was calculated based on household characteristics and durable assets using the World Bank method [39, 40].
Baseline Woman’s body mass index Woman’s weight was measured using a portable digital weighing scale. Height was measured against the smooth but hard wall. Height and weight were used to calculate body mass index using international formula (weight/height2). It was used as a continuous variable to examine its associations with other covariates.
Baseline Reproductive health Study-specific questions adapted from our prior research [39] about gravidity, parity, prior spontaneous/induced abortions, pregnancy intention, taking iron tablets during current pregnancy, foetal health, sex of index foetus and a number of children.
Baseline History of psychiatric illness Single yes/no question was used to assess if the participant had been diagnosed with or treated for any psychiatric illness within last year.
  Intimate partner relationship  
Baseline Quality of relationship with the current intimate partner The Relationship Assessment Scale (RAS) comprises 7 items scored from 1 to 5 and total scored from 7 to 35. Mean inter-item correlation of the scale is 0.49; test-retest reliability (among undergraduate students in USA) is 0.85 and high correlation with Dyadic Adjustment Scale [41] (0.86 to .88). Examples of items are: ‘How well does your partner meet your needs? In general, how satisfied are you with your relationship? How much do you love your partner?’ Higher scores indicate a better quality of the relationship [42].
Baseline Experiences of intimate partner violence Items from the World Health Organization Multi-Country Study on Women’s Health and Violence Against Women Questionnaire, including lifetime experiences of controlling behaviour (7 items), emotional (4 items), physical (6 items), and sexual (3 items) violence by the current intimate partner [43]. Any lifetime experiences of intimate partner violence calculated combining any of four sub-types of violence.
Baseline Practical and emotional support specific to the earthquakes Study-specific questions adapted from previous studies [10, 20]. Participants were asked whether they received any support including shelter, food, clothes, informal emotional and professional psychological support and rescue from the hazardous place during/after earthquakes by any individual or any governmental and non-governmental organization.