These participants had uterine artery Doppler investigations, as part of a routine scan between the 18th and the 22nd week of pregnancy. The investigators were blinded to the results of the biochemistry results.
All samples of the tHcy measurement were collected between 15 and 19 weeks of gestational age, as calculated from the last menstrual period or from early ultrasound dates (when the menstrual dates differed from the specified gestation). The plasma tHcy concentrations were measured by means of a fluorescence polarization immunoassay (9).
Uterine artery flow velocity waveforms were obtained using an SD 800 Doppler system (Philips Medical Systems, Gland, Switzerland) with a 3.5/5-MHz linear array probe. The high-pass filter was set at 100 Hz. One operator performed the measurements. The use of mean resistance index (RI) cutoff points with bilateral and unilateral notches has already been shown to improve the efficacy of uterine artery Doppler screening using qualitative assessment (10). A screen-positive or abnormal result was defined as bilateral notches and a mean RI \>0.55 (50th centile), unilateral notches and a mean RI \>0.65 (80th centile), and absence of notches and a mean RI \>0.7 (95th centile) (11). Women with these abnormal results were offered growth scans, amniotic fluid volume assessment, and umbilical artery Doppler every 4 weeks until 36 weeks in view of the recognized increased risk of isolated IUGR (12), unless there were other clinical indications, which necessitated closer surveillance
