Methods
Sampling method and sample size
The data was derived from a 2006 cross-sectional household survey which assessed and compared the predictors of risk of alcohol-exposed pregnancies among women (18–44 years old) from two contrasting sites; a rural and urban site in South Africa [17]. Participants were recruited from an urban area (N = 606) located in the Tshwane Metropolitan Municipality in the Gauteng region and a rural area (N = 412) in the West Coast district of the Western Cape. The two provinces are broadly similar in level of socio-economic wealth, age/gender structure and disease burden outcome and the different sites were chosen primarily for urban/rural difference and for differences in race composition. Cluster random sampling was used at the urban site with a target sample size of 820 women. Random selection was used to select 82 census enumeration areas (EA) out of 450 areas; from each EA, 10 households were then selected using aerial photographs. One woman was selected randomly within each household, provided she met the eligibility criteria after a brief household census identified all adults in the housheold 18 years or older. Stratified cluster random sampling was used at the rural site with a target sample size of 650 women. Farms were chosen within the boundaries of the three municipal areas. Out of 1450 farms listed, 150 farms were randomly selected. All eligible women on each farm were approached to participate in the study to improve recruitment as there were generally a small number of households per farm (approximately 7).
Trained fieldworkers conducted face-to-face interviews using structured questionnaires in the participant’s preferred language from a choice of five common languages among the study population. The questionnaire contained measures which have largely been used previously in similar populations in South Africa. The interviews took between 15 and 90 min and were conducted in the privacy of the participant’s home. In total, 606 women were interviewed in urban site and 412 women were interviewed in the rural site corresponding to response rates of 74 % and 83 % respectively [17].
For the purposes of this study, only women who had ever been pregnant were eligible and therefore data of women who had never been pregnant ie; never given birth or had never had a miscarriage were excluded. Women who reported being currently pregnant were only included in the study provided this was not their first pregnancy i.e., this study focused only on information about the pregnancy of their last born child and not their current pregnancy. A total of 363 women (13 of whom were also currently pregnant) from the rural sample and 466 women (14 of whom were also currently pregnant) from the urban site met the inclusion criteria for the current study (Fig. 1).