- Pregnancy creates a unique situation in which both vasculogenesis and extensive angiogenesis are required for successful fetal and placental development. Recently, the soluble form of vascular endothelial growth factor (VEGF) receptor-1 (sVEGFR-1), an antagonist to VEGF and placental growth factor (PlGF) (two important angiogenic factors), has been implicated in the pathophysiology of preeclampsia and small for gestational age (SGA) without preeclampsia. There is, however, a paucity of information concerning plasma sVEGFR-1 concentrations in other obstetrical disorders. The purpose of this study was to determine plasma sVEGFR-1 concentrations in normal pregnancy, term gestation in labor, and in patients with pregnancy complications including spontaneous preterm labor, preterm premature rupture of the membranes (PROM), fetal death, and acute pyelonephritis. A cross-sectional study was conducted to determine the concentrations of sVEGFR-1 in plasma obtained from 499 women in the following groups: (1) non-pregnant women (n = 40); (2) pregnant women (n = 135); (3) normal pregnant women at term in labor (n = 60); (4) fetal death (n = 60); (5) spontaneous preterm labor with intact membranes (n = 102); (6) preterm PROM (n = 64); and (7) pregnancy with acute pyelonephritis (n = 38). Since plasma sVEGFR-1 concentration changes with gestational age, the difference between the actual and the expected plasma sVEGFR-1 concentration (derived from regression equation of normal pregnancy) for each patient (delta value) was calculated and used to examine the differences of plasma sVEGFR-1 concentrations among various groups. Plasma concentrations of sVEGFR-1 were determined by enzyme-linked immunoassay. Regression analysis and non-parametric statistics were used for analysis. (1) Normal pregnant women before term had a median plasma sVEGFR-1 concentration significantly higher than non-pregnant women (p < 0.001); (2) plasma sVEGFR-1 concentration increased with advancing gestational age in normal pregnancy (r = 0.5; p < 0.001); (3) there was no significant difference in the median delta plasma concentration of sVEGFR-1 between normal pregnant women at term with and without labor (p = 0.09); (4) patients with fetal death had a median delta plasma concentration of sVEGFR-1 significantly higher than normal pregnant women (p = 0.001). Among patients with fetal death, those with unexplained causes (p = 0.04) and those with preeclampsia (p < 0.001) had a significantly higher delta plasma sVEGFR-1 concentration than normal pregnant women; and (5) there was no significant difference in the median delta plasma sVEGFR-1 concentration between normal pregnancy and preterm labor with intact membranes, preterm PROM (regardless of the presence or absence of microbial invasion of the amniotic cavity), or acute pyelonephritis (all p > 0.05). Plasma sVEGFR-1 concentration is increased in a subset of patients with fetal death, but does not change in term and preterm parturition, rupture of fetal membranes, or acute pyelonephritis.