Material and Method: The present prospective cohort study recruited the normal singleton pregnant women at 16 to 24 weeks gestation who had antenatal care and midtrimester ultrasound screening at Ramathibodi Hospital between June and September 2012. Transvaginal ultrasound (TVU) measurements of cervical length (CL), cervical volume (CV), vascularization index (VI), flow index (FI), and vascularization flow index (VFI) were performed. The pregnant women with multifetuses, severe fetal anomalies, unknown delivery status, abortion, stillbirth, and preterm birth were excluded from the present study.

Results: The authors recruited 168 cases but 25 cases were excluded. Only 143 cases were included into the study. The mean of gestational age at ultrasound examination and delivery was 21 and 39 weeks respectively. There were no perinatal morbidity and mortality in the present study. The average values of cervical profiles of CL, CV, VI, FI, and VFI were 4.2 cm, 31.6 cm3, 6.4, 38.9, and 2.6 respectively.

Conclusion: The normal reference of cervical blood perfusion in Thai pregnant women was established. The VI, FI, and VFI of the normal term singleton pregnancy at 16 to 24 weeks gestation were 6.4, 38.9, and 2.6 respectively.

Keywords: Cervical length (CL), Cervical volume (CV), Cervical blood perfusion, Fractional moving blood volume (FMBV), Power Doppler-flow indices, 3D transvaginal ultrasound, VOCAL, Preterm birth (PTB)