Study population and design
The data for this study were derived from prospective screening for adverse obstetric outcomes in women attending for routine pregnancy care at 19+0-24+6 weeks’ gestation at King’s College Hospital and Medway Maritime Hospital, UK, between 2011 and 2020. In this visit we first, recorded maternal demographic characteristics and medical history as self-reported by the patients, second, carried out an ultrasound examination for fetal anatomy and measurement of fetal head circumference, abdominal circumference and femur length to calculate the EFW by the Hadlock formula9, because a systematic review identified this as being the most accurate model 10, and third, measured the left and right UtA-PI either by transvaginal or transabdominal color Doppler ultrasound and calculated the mean value of the two arteries11,12. The majority of UtA-PI measurements were carried out transvaginally because at the same time we were measuring cervical length; the transabdominal approach was used when women declined transvaginal sonography. Gestational age was determined from measurement of fetal crown-rump length at 11-13 weeks or the fetal head circumference at 19-24 weeks13,14. The same study population was used for development and validation of the model based on multivariable logistic regression analysis for prediction of placental dysfunction related stillbirth1.
The inclusion criteria for this study were singleton pregnancies that delivered a phenotypically normal live birth or stillbirth at> 24 weeks’ gestation. We excluded pregnancies with known aneuploidies, major fetal abnormalities, those ending in a miscarriage or termination of pregnancy. There was no patient involvement in the design of the study.