Strengths and limitations
This study had several strengths and limitations. Strengths were the
novel statistical methods, the large availability of variables and the
large and representative sample. Inclusion in Generation R was aimed at
the first trimester, but was still possible until birth ensuring that
those with a late antenatal care initiation were still
eligible.20 Some limitations should also be taken into
account. We were limited by self-report of pregnancy recognition. This
may be subject to recall bias or socially acceptable answers, which may
have diluted the associations. In addition, as mentioned in the methods
section, one of the assumptions of this causal study design is
consistency, which means that the hypothetical intervention (early
pregnancy recognition) must be well-defined. In practice, an
intervention that ensures everyone will recognize the pregnancy within 6
weeks does not exist. In the third paragraph of the discussion we
explained that varying reasons may complicate timely recognizing a
pregnancy, therefore potentially violating the consistency assumption.
To reduce the possibility of bias, we performed sensitivity analyses in
those with a regular cycle, because they would be more likely to know
when they miss their period. The results indicated that the reductions
in inequalities in antenatal care initiation were only significant for
pregnancy intention, migration background and neighborhood deprivation,
showing that our initial results may have been slightly overestimated.