['To examine early midtrimester amniotic fluid for its significance in pregnancy outcomes, especially with connection to the pathogenesis of preeclampsia.', 'A prospective, nested, case-control study was conducted. Fetal fibronectin in early midtrimester (16-20 weeks gestation) amniotic fluid was measured by EIA method. Results were compared by their pregnancy outcomes.', 'Amniotic fluid levels of fetal fibronectin were significantly higher in the group subsequently developing severe preeclampsia (106.8 +/- 13.2 micrograms/ml, mean +/- SD, n = 12) compared with matched controls (66.7 +/- 7.1 micrograms/ml, n = 12) (p < 0.05).'] Is elevated fetal fibronectin in midtrimester amniotic fluid involved with the onset of preeclampsia?