For the prediction of late-onset preeclampsia (PE) in low risk women, the investigators established a cut-off value for sFlt-1/PlGF ratio and evaluated the combination models of Elecys, second trimester uterine artery (UtA) doppler, and fetoplacental proteins for Down syndrome screening.

A prospective study was carried on in Cha hospital. Serum samples for Down syndrome screening were assayed to estimate pregnancy-associated plasma protein-A (PAPP-A), alpha-fetoprotein , unconjugated estriol, human chorionic gonadotrophin , and inhibin-A. Women screened for Down syndrome were offered UtA Doppler at 20-24 weeks of gestation and then collected serial serum samples for sFlt-1/PlGF ratio at two time points (24-27 and 34-37 weeks' gestation).

Inclusion Criteria:

• Women considered as a potential participant in this research were patients regularly visited at the prenatal care of Cha hospital in Seoul, Korea

Exclusion Criteria:

• early onset and cases not to measure the sFlt/PlGF ratio and other markers
• twin pregnancy
• Chronic hypertension
• prior history of preeclampsia
• pregestational diabetes mellitus
• gestational diabetes mellitus
• patients delivered before 35 weeks of gestation
• preeclamptic patients with onset before 35 weeks of gestation
• patients with body mass index 25kg/m2 or greater
• maternal age 40 years older

low risk women who had not a risk factor of preeclampsia.