This prospective, nested, case-control study investigated whether maternal plasma fetal fibronectin reflects reduced trophoblastic invasion at 16 to 20 weeks in women who later have preeclampsia. Concentrations of fetal fibronectin were 8.7 +/- 2.6 micrograms/ml in women with preeclampsia and 8.1 +/- 2.5 micrograms/ml in matched controls (p greater than 0.5). These results are discussed.