Study design and participants
The data were derived from prospective screening for pregnancy complications in women with singleton pregnancies attending their first routine hospital visit at 11 + 0 to 13 + 6 weeks of gestation at King’s College Hospital, London or Medway Maritime Hospital, Kent from March 2006 to November 2020. The visit included recording of maternal demographic characteristics and medical history, measurement of maternal weight and height and ultrasound examination for the measurement of the fetal crown–rump length (CRL) and to determine gestational age24, measurement of the fetal nuchal translucency thickness, as part of screening for trisomies25, and examination of the fetal anatomy for the diagnosis of major fetal defects26.
Participants completed a questionnaire, which was then reviewed by a doctor together with the woman. Patient characteristics included maternal age, racial origin (white, black, South Asian, East Asian, and mixed), method of conception (natural or assisted by IVF or use of ovulation drugs), cigarette smoking during pregnancy, medical history of chronic hypertension, diabetes mellitus, systemic lupus erythematosus (SLE) or antiphospholipid syndrome (APS), family history of preeclampsia in the mother of the patient, and obstetric history that included parity (parous or nulliparous if no previous pregnancies at ≥24 weeks’ gestation), previous pregnancy with PE and previous pregnancy with delivery of small for gestational age (SGA) neonate with birth weight <10th percentile of The Fetal Medicine Foundation fetal and neonatal population weight charts.27
The inclusion criteria for this study were singleton pregnancies delivering a non-malformed live birth or stillbirth at ≥24 weeks’ gestation. We excluded pregnancies with aneuploidies and major fetal abnormalities. Women gave written informed consent to take part in the study which was approved by the NHS Research Ethics Committee. There was no patient involvement in the design of the study.