Biochemical analysis
Blood glucose and insulin were analysed with a Cobas Modular system (Roche Diagnostics, Risch, Switzerland) at the Clinical Chemistry Laboratory, Sahlgrenska University Hospital (accredited in accordance with the International Standard ISO 15189:2007). HOMA-IR was calculated as (fasting glucose × fasting insulin)/22.5 and HOMA-B as (20 × fasting insulin)/(fasting glucose − 3.5)25. GDF15 was analysed with an ELISA (Human GDF-15 Quantikine Elisa Kit, R&D Systems, Minneapolis, MN, USA); serum samples during and after pregnancy were diluted 1:64 and 1:4, respectively. The intra- and inter-assay CVs for GDF15 measurements were 1.7% and 7%, respectively.