Beeckman et al. BMC Public Health 2010, 10:527 http://www.biomedcentral.com/1471-2458/10/527 Page 2 of 9 Figure 1 outline of the behaviour model by Andersen and Newman [17], reflecting individual determinants included in the analyses. Newman [17,24]. With regard to the individual determi- nants, the predisposing component refers to the charac- teristics of the person and includes demographic, social position and attitudinal variables [17,24]. The enabling component consists of conditions that make health care use available to the person [17,24]. The third compo- nent, ‘illness level’, is most directly related to health care use and comprises perceived illness and diagnosed ill- ness [17,24]. In the context of our study, ‘illness level’ can be translated to pregnancy history and the current course of the pregnancy. Our study examines the use of antenatal care in the Brussels metropolitan region. It can be assumed that the health care context was the same for all women in this region and that the organization of antenatal care was also similar. Consequently, the effect of variation in health care systems as defined by Andersen and New- man is limited. We therefore decided to focus on indivi- dual determinants which influence health care use directly [17,24]. The aim of this study is to measure the effect of predisposing, enabling and pregnancy-related factors on the use of antenatal care. Methods Data collection A prospective observational study of antenatal care use was conducted in the Brussels Metropolitan region. Women were recruited consecutively in nine of the ele- ven antenatal clinical centres spread over the region. During pregnancy each woman is referred to one of these centres for their ultrasound screening. The inclu- sion criteria were: having a gestational age of less than sixteen weeks or attending the third antenatal visit or less, residing in the Brussels Metropolitan Region, aged over eighteen years and being able to speak Dutch, French, English, Turkish or Arabic (these languages cover 95.5% of the Brussels population [25]). The exclu- sion criteria were: multiple pregnancies, existing medical problems (heart disease, diabetes, hypertension or renal diseases for instance), no informed consent and not being reachable by phone. We obtained ethical approval from all participating sites and from the Ethics Commit- tee of the University Hospital UZ Brussel, prior to the start of the study. At the moment of recruitment, a first questionnaire about personal characteristics and pregnancy history was filled out. Any antenatal visit prior to recruitment was documented by structured interview. Additionally, all participating women received a diary, developed to record every antenatal visit in a standardised manner. The researcher explained how to use the diary and a manual was provided. Various alternatives of data col- lection were considered, like use of medical files or data registers. These options were lacking the level of detail required or were not reliable for our study. Use of a diary enabled us to record every visit, even when the women change from care provider or care setting. Bimonthly telephone follow-up interviews were con- ducted to record the antenatal care use and to verify the completeness of the data. Variables An antenatal visit was defined as a contact with a health care professional to follow up pregnancy. Antenatal care can be provided by an obstetrician, midwife or general- ist. If the woman visited more than one professional at the same place on the same day, this was counted as one visit. Separate visits to the laboratory for a blood sample and/or urine test were not counted as an antenatal visit. The total number of visits was analysed in association with predisposing, enabling and pregnancy related char- acteristics and presented in figure 1. The mother’s age, marital status, origin, educational level and activity sta- tus were the predisposing variables examined. The following enabling factors were considered in the analyses: having health insurance coverage, receiving welfare benefits, having a regular obstetrician and/or regular generalist, equivalent income. Equivalent income was calculated using the modified Organization for Eco- nomic Co-operation and Development (OECD) scale [26], based on the monthly household income and household composition. The women were regrouped