28 CHAPTER 2 and adverse birth outcome, but neglected co-existence of both protective- and risk factors that can influence outcomes (12, 18, 19). The aim of this study was to identify classes of vulnerability among pregnant women based on a wide range of social risk and protective factors in a latent class analysis (LCA). We conducted the LCA using Dutch observational nationwide data sources and self-reported data prior to pregnancy. In addition, we validated these classes by studying the association between latent class membership and various maternal and perinatal health outcomes and care utilization. METHODS Data sources This study utilized data from the nationwide population-based data infrastructure DIAPER (acronym for Data-InfrAstructure for ParEnts and childRen). DIAPER integrates routinely collected observational data from three Dutch nationwide data sources (Perined, Vektis and Statistics Netherlands) at individual level. The Dutch Perinatal Registry ‘Perined’ collects routine care data on pregnancy after 22 weeks of gestation, birth and the first 28 days after birth, as supplied by midwives, gynaecologists and paediatricians (20). Healthcare information centre ‘Vektis’ collects claims data under the Dutch Healthcare Insurance Act and provides data on healthcare utilization and spending (21). ‘Statistics Netherlands’ collects and publishes data on societal matters and provides access to data through their System of Social Statistical Datasets (SSD) (22, 23). This linkable SSD-data covers nearly 20 themes, including health, welfare, income, education and labour. We enriched DIAPER with self-reported data on health, well-being and lifestyle of the Public Health Monitor 2016 (PHM-2016) (24). This is a health survey among a varying sample of the Dutch population aged 19 years and older, carried out every 4 years by the Community Health Services, Statistics Netherlands and the National Institute for Public Health and the Environment. The PHM-2016 had 457.153 participants and was mainly conducted from September-December 2016. Appendix A provides more information about the data sources. Study population To ensure that information was not influenced by pregnancy itself, women were eligible for inclusion if these criteria were met: (i) they participated in the PHM-2016 (pre-pregnancy), (ii) they gave birth (livebirth or stillbirth) or had a termination of pregnancy before 1 January 2019, and (iii) pregnancy data in 2017 or 2018 were recorded within Perined. In case women had multiple pregnancies or births during the study period, only data on the first observation was included, to avoid duplication of women’s characteristics.
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