Inter- and Intra-observer Variability in First-trimester Uterine Artery Doppler Measurements.

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).