Methods
For registrations to all pregnancy related events, we retrieved information from Statistics Denmark. Statistics Denmark holds copies of several national registries including the National Patient Registry, which registers all in- and outpatient contacts in Denmark, including procedural codes and dates of contact, using International Classification of Diseases (ICD), 8th or 10th edition. Statistics Denmark utilized the civil registration number and identified our Marfan syndrome women in the registries and ensured identification of 100 age matched (year of birth) female controls as well as accurate linkage of data. For two Marfan syndrome women, no controls were given, thus, data were obtained for 195 Marfan syndrome women and their 19,500 controls, matched on age and region.
Statistics Denmark holds no clinical data, for instance on aortic size and blood pressure.