The aim of this study is to investigate the inter- and intra-observer variability of first-trimester Uterine Artery Doppler ultrasound measurements in pregnancies between 11+0 and 13+0 weeks of gestation. Participants will undergo a measurement protocol (six sets of Doppler ultrasounds measurements of right and left uterine artery) performed alternately by two observers (sonographers or physicians who perform these ultrasounds frequently in clinical practice at the outpatient clinic).

Doppler ultrasound measurements are increasingly performed in clinical practice to detect high-risk pregnancies. First-trimester uterine artery Doppler measurement might be a potential predictor for the development of maternal hypertensive disorders later on in pregnancy. However, before implementing this measurement into clinical practice and prediction models, the test characteristics of this first-trimester Doppler measurements should be adequately studied. The objective is to assess the inter- and intra-observer variability of first-trimester uterine Doppler ultrasound measurements.

Inclusion Criteria:

• Singleton pregnancy
• Gestational age from 11+0 weeks to 13+6 weeks

Exclusion Criteria:

• Maternal age <18 years

  • Inability to give informed consent
  • Multiple pregnancy
  • Abnormal fetal heart tracings
  • Non-viable pregnancy

All women with a first-trimester singleton pregnancy receiving a Doppler ultrasound at the outpatient clinic are eligible.