The aim of this study was to identify pregnant women at risk of preeclampsia (PE) before clinical manifestations appeared using a panel of serum markers. We recruited 240 consecutive women who presented for antenatal care. We investigated whether serum levels of placental growth factor (PlGF), its inhibitor, soluble fms-like tyrosine kinase-1 (sFlt-1), measured at 13–16 weeks gestation and the expression of fms-like tyrosine kinase-1 (Flt-1) in the maternal neutrophils measured by flow cytometry could be predictive of the subsequent development of PE. Serum PlGF levels were found to be significantly lower among women who developed PE than patients with gestational hypertension or patients in the control group (p < 0.001). In contrast, serum sFlt1 levels were most elevated in patients who developed PE versus those with gestational hypertension or the control group (p < 0.001). Serum levels of neutrophil-Flt-1, however, were lower in women who developed PE than in those with gestational hypertension or those in the control group (p < 0.001). Increased serum levels of sFlt-1, decreased levels of neutrophil-Flt-1, and decreased levels of PlGF may predict women at risk of developing PE later in pregnancy.