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.