Predictors for uptake of intermittent preventive treatment of malaria in pregnancy (IPTp) in Tanzania

Cross-sectional survey of nationally representative sample of individuals aged 15–49 years living in Tanzania in the period between December 2011 and May 2012.

The study was based on data from the 2011/12 Tanzania HIV and Malaria Indicators Survey (THMIS), conducted by the National Bureau of Statistics (NBS) in collaboration with the Tanzania Commission for AIDS (TACAIDS) and the Zanzibar AIDS Commission (ZAC), the Ministry of Health and Social Welfare (MoHSW) and the USAID-funded MEASURE DHS project from December 16, 2011, to May 24, 2012.

The sampling frame used for the 2011–12 THMIS was developed by the National Bureau of Statistics (NBS) after the 2002 Population and Housing Census (PHC) which covered all of the 30 regions of Tanzania. The sampling frame excluded nomadic and institutional populations such as persons in hotels, barracks, and prisons. The sample was selected in two stages. The first stage involved selecting sample points (clusters) consisting of enumeration areas (EAs) delineated for the 2002 PHC. A total of 583 clusters were selected. On the Mainland, 30 sample points were selected in Dar es Salaam and 20 were selected in each of the other 24 regions. In Zanzibar, 15 sample points were selected in each of the five regions. The second stage of selection involved the systemic sampling of households. A household listing operation was undertaken in all the selected areas prior to the fieldwork. From these lists, households to be included in the survey were selected. Approximately 18 households were selected from each sample point for a total sample size of 10,496 households. Weighting factors were added to the data file so that the results will be proportional at the national level. All women and men age 15–49 who were either permanent residents of the selected households or visitors who stayed in the household the night before the survey were eligible to be interviewed.

Two questionnaires were used for the 2011–12 THMIS: the Household Questionnaire and the Individual Questionnaire. These questionnaires are based on the MEASURE DHS standard AIDS Indicator Survey and Malaria Indicator Survey questionnaires and were adapted to reflect the population and health issues relevant to Tanzania. The questionnaires were translated into Kiswahili; the national language of Tanzania. Data presented in this study is based on the individual questionnaire.

Completed interviews were obtained for 10,967 women, yielding a response rate of 96 %. Of the 9,388 eligible men identified, 8,352 were successfully interviewed (89 % response rate). The principal reason for non-response among both eligible women and men was the failure to find them at home despite repeated visits to the households.

Questions regarding malaria in pregnancy were administered to women who have had a pregnancy in the past 5 years before the survey. To control recall bias we selected 3,555 women with a live birth 2 years prior to the survey out of the 10,967 women who completed the interviews. IPTp uptake was verified on the antenatal card, therefore only women with a live birth in the past 2 years and who attended antenatal services were included.

Out of the 3,555 women, 1,809 were excluded with 1,746 women remaining who had their antenatal cards at the time of survey as a proof of antenatal care attendance during pregnancy. Further, 130 women were excluded for lack of information about uptake of IPTp remaining with a sample of 1,616 women who were included in this study (Fig. 1).

Guided by literature review, useful variables were identified from the 2011–12 THMIS Individual questionnaire. A conceptual framework was developed comprised of a list of primary independent variables (such as socio-economic and demographic variables), modifiable variable/intermediate independent variables, which are variables that could potentially be affected by the primary independent variables (such as number and timing of antenatal visits as well as birth under professional assistance) and lastly the outcome variable.

Uptake of IPTp was the outcome variable of interest defined as uptake of the recommended two or more doses of IPTp; one during the second trimester and the second during the third trimester (WHO, 2003). Women who did not take or took less than the recommended number of dosage were categorized as having low uptake of IPTp.

This study included several socioeconomic and demographic variables that have been theoretically and empirically linked to malaria in pregnancy and uptake of IPTp. Participants’ age was categorized as follows: 15–24, 25–34, and 35–49 years of age. The participant’s area of residence was categorized as being rural or urban. The education level of women was categorized as follows; no education, primary incomplete, primary complete and secondary or higher education. We categorized a woman’s marital status into never married, separated/widowed and married. Occupation was categorized as unemployed, self employed and employed. Participant’s wealth index was categorized as follows: poorest, poorer, middle income, richer and richest. The wealth index is constructed using household asset data, including ownership of consumer items ranging from a television to a bicycle or car, as well as dwelling characteristics, such as source of drinking water, sanitation facilities, and type of flooring material. The wealth index was created in three steps. In the first step, a subset of indicators common to urban and rural areas was used to create wealth scores for households in both areas. In the second step, separate factor scores were produced for households in urban and rural areas using area-specific indicators. The third step combined the separate area-specific factor scores to produce a nationally applicable combined wealth index by adjusting area-specific scores through a regression on the common factor scores. The resulting combined wealth index has a mean of zero and a standard deviation of one. Wealth quintiles (from lowest to highest) were formed by assigning the household score to each participant, ranking each person in the study by that score, and then dividing the ranking into the five wealth index quintiles. We included parity defined as a woman’s number of live births that were categorized as: no child, 1 child, 2 children, and 3+ children. We further categorized Tanzania into nine zones, which tend to have different seasons and malaria prevalence. The zones included Eastern, Western, Southern, Southern High, South West Highlands, Central, Northern, Lake and the Zanzibar zone.

We also included intermediate factors potentially related to the uptake of IPTp and malaria in pregnancy. We categorized access to information about malaria whether a woman ever heard or never heard about IPTp (yes or no). We assessed access to antenatal services by including two variables; timing of the 1st Antenatal visit and the source of anti-malarias during the most recent pregnancy prior to the survey. Participant’s timing of the 1st Antenatal visit was categorized as being in; 1st trimester, 2nd trimester or 3rd trimester. Source of anti-malarias was categorized as antenatal centers or other sources.

We calculated descriptive statistics for sample’s socio-demographic characteristics and IPTp uptake. Chi-square test was used to assess socio-demographic differences in IPTp uptake. The level of significance was set at P < 0.05 (2-tailed) for all the analyses. Both bivariate and multiple logistic regression were used to generate crude (OR) and adjusted odds ratios (AOR). Odds ratios were estimated to assess the strength of the associations and used the 95 % confidence intervals (CIs) for significance testing. All the covariates which showed statistically significant relationship (P < 0.05) with the outcome variable after Chi-square test were entered simultaneously into the multiple regression model. Analyses were performed using SPSS version 16. Sample weighting was applied to allow for adjustments for the cluster sampling design and sampling probabilities across clusters and strata.

Data collection procedures for the THMIS were approved by Tanzania’s National Institute for Medical Research (NIMR), the Zanzibar Medical Ethics and Research Committee (ZAMREC), the Institutional Review Board of ICF International, and the Centers for Disease Control and Prevention in Atlanta. The protocol of the survey was reviewed and approved by the Tanzania’s National Institute for Medical Research (NIMR), the Zanzibar Medical Ethics and Research Committee (ZAMREC), the Institutional Review Board of ICF International, and the Centers for Disease Control and Prevention in Atlanta. All the participants were asked to provide verbal informed consent after being read a document emphasizing the voluntary nature of the survey. Interviews were conducted under the most private conditions afforded by the environments encountered. If privacy could not be ensured, the interviewers were instructed to skip the module.