Predictors
The variables age, relationship status, migration background, pregnancy intention, mental health problems, Dutch language skills and parity have previously been identified as predictors for late antenatal care initiation.9-13 Other variables are socioeconomic factors, such as education, employment household income, housing and neighborhood deprivation.14 In addition, we studied cognitive functioning, because this is related to someone’s health literacy skills.24
Individual predictors
Age at conception was calculated as age at birth of the child minus gestational age at birth and categorized into <20 years, 20-25 years, 25-30 years, 30-35 years and ≥35 years. The following predictors were measured by questionnaire in the 12th week of gestation, or during enrollment in case participation started after the 12th week of gestation. Migration background was defined as one or both parents being born in another country than the Netherlands, according to the classification of Statistics Netherlands.25 This was categorized into first- or second-generation migrant depending on whether or not the woman herself was born in the Netherlands.23, 26 Relationship status was categorized as being married or cohabiting, versus single. Pregnancy planning was measured using self-report by asking whether the pregnancy was planned or not. In the case of an unplanned pregnancy, women reported how they felt about the pregnancy using the following four answering categories: “pleased from the start”; “initially mixed feelings”; “still mixed feelings”; or “mostly unhappy about the pregnancy”. Pregnancy intention was categorized into planned, unplanned and wanted from the start and unplanned with ambivalent feelings. History and current mental illness were assessed at 20 weeks’ gestation using vignettes explaining depression, anxiety, psychosis, eating disorders and addiction to substances, followed by questions about whether the women had ever experienced these symptoms and received treatment for them, and whether these symptoms were present in the past year. Mental illness was defined as either depression, anxiety, psychosis, eating disorders or substance use addiction and categorised into recent, when the symptoms were present in the last year, or ever, when the symptoms occurred in their lifetime, but not in the last year. Proficiency in Dutch language skills was measured by a questionnaire in week 30 of gestation. The pregnant women were asked to rate their Dutch speaking, reading, and writing skills on three separate 5-point scales ranging from ‘not at all’ (1) to ‘good’ (5). This information was summed into general ‘Dutch language skills’ (1–9, not good; 10–14, reasonable; 15, good). 27 Parity was based on medical records and categorized into nulliparous or multiparous.
Socioeconomic predictors
The following predictors were measured by questionnaire in the 12th week of gestation. Education was defined as the highest attained educational level, categorized as: Low (primary school; lower vocational training; intermediate general school; 3 years general secondary school), which typically corresponds to ≤12 years of education; Medium (>3 years general secondary school; intermediate vocational training; higher vocational training; Bachelor’s degree), in general corresponding with 13–17 years of education; and High (higher academic education; PhD), usually indicating 18 years of education or more. Employment was categorized into having a paid job (including being self-employed) versus having no paid job. Net household income was categorized as: Less than \euro1200/month (social security level at the time of assessment); Between \euro1200 and 2000/month; and More than \euro2000/month (modal income or more). Housing was measured by a questionnaire in week 30 of gestation and categorized into living in a bought or rented home. Neighbourhood deprivation was measured using area-based status scores provided by the Netherlands Institute for Social Research (in Dutch: Sociaal en Cultureel Planbureau).28 The scores were matched on four-digit postcodes and are based on mean household income, proportion of the population with low income, proportion of population with low educational attainment and proportion of population without paid work.29 The scores were categorized into tertiles (low, medium and high deprivation). Cognitive functioning was measured using the 12-item validated short version of the Raven’s Progressive Matrices at the research center when the child was 5 years old.30 This was categorized into <70 (mild intellectual disability), 70-85 (borderline intellectual functioning) and ≥85 (normal intellectual functioning).31 We expect that this measure is relatively stable, and not influenced by the timing of antenatal care initiation.