This is an international multicentre prospective cohort study to validate the Bayes theorem based algorithms for the screening of pre-eclampsia (PE) in the first-trimester of pregnancy.

The investigators have previously constructed Bayes model in the first-trimester which combines maternal characteristics and medical history (Mat-CH) together with mean arterial pressure (MAP), uterine artery pulsatility index (PI), and serum placental growth factor (PlGF) with a plan to assess the predictive performance.

The reference standards will be PE defined according to the International Society for the Study of Hypertension in Pregnancy and the American College of Obstetricians and Gynecologists. The systolic blood pressure should be >140 mm Hg and/or the diastolic blood pressure should be >90 mmHg on at least two occasions four hours apart developing after 20 weeks' gestation in previously normotensive women and there should be proteinuria (>300 mg in 24 hours or two readings of at >2+ on dipstick analysis of midstream or catheter urine specimens if no 24-hour collection is available). In the absence of proteinuria, new onset of any of the following systemic findings: a) thrombocytopaenia (platelet counts <100,000 µL); b) renal insufficiency (creatinine >1.1 mg/dL or 2-fold increase in creatinine in the absence of underlying renal disease); c) abnormal liver function (ie, hepatic transaminase levels twice normal); d) pulmonary oedema; or e) cerebral or visual symptoms. Preterm-PE is PE that requires delivery before 37 weeks' gestation. If a participant fulfills the criteria for PE by one definition and not the other she will be considered to have developed PE.

Inclusion Criteria:

• Aged ≥ 18 years
• Singleton pregnancy
• Live fetus
• Provide Informed and written consent in the official language of the country

Exclusion Criteria:

• Unable to provide written Informed consent learning difficulties or serious mental illness or an inability to understand spoken and written the official language of the country.
• Multiple Pregnancy
• Non-viable fetus (missed spontaneous abortion or stillbirth)

All eligible women attending for their hospital visit at 11-13 weeks will be invited to participate.