A longitudinal study of plasma levels of soluble fms-like tyrosine kinase 1 (sFlt1), placental growth factor (PlGF), sFlt1: PlGF ratio and vascular endothelial growth factor (VEGF-A) in normal pregnancy.

Objective: To describe plasma levels of angiogenic (PlGF, VEGF-A) and anti-angiogenic (sFlt1) factors as well as the sFlt1:PlGF ratio throughout normal pregnancy and postpartum.

Design: Longitudinal prospective study.

Setting: One outpatient antenatal clinic in Uppsala, Sweden.

Population: Thirty-seven healthy women with normal pregnancies and normal neonatal outcome were included.

Methods: Blood samples were collected from each woman at least six times. Plasma levels of sFlt1, PlGF and VEGF-A were measured using commercially available ELISA kits.

Main Outcome Measures: Median plasma levels, the 25th to the 75th percentile and the average change per gestational week of sFlt1, PlGF and the sFlt1:PlGF ratio.

Results: sFlt1 levels were relatively constant until weeks 29-30, when they increased, reaching a peak at week 40. An increase of 643pg/ml per week was observed from weeks 30 to 40. Postpartum levels were low. PlGF increased by 16pg/ml per week from early pregnancy until weeks 29-30 and thereafter decreased by 14pg/ml per week until week 40. The sFlt1:PlGF ratio decreased from weeks 9-12, was constantly low from weeks 19-20 to 37-38 and then increased to weeks 39-40. VEGF-A was detectable in only 8% of the samples during pregnancy and in 64% postpartum.

Conclusion: This longitudinal study demonstrates how sFlt1, PlGF and the sFlt1:PlGF ratio fluctuate throughout normal pregnancy and postpartum and may serve as a reference against which these factors can be studied in complicated pregnancies. VEGF-A levels were more often detectable postpartum.