Objective : To establish the reference ranges for first trimester umbilical cord and vessel diameters of Thai fetuses.
Material and Method : A prospective study was performed on normal pregnant women between 10+0 and 13+6 weeks of gestation who underwent ultrasound examination. The diameter measurements were obtained by a 7.5 MHz vaginal - or a 3.75 MHz abdominal transducer. Statistics were analyzed using SPSS computer program.
Results : Records of 184 pregnancies were analyzed and the outcome demonstrated a strong correlation between umbilical cord diameter and gestational age (r = 0.90; p < 0.001). Umbilical vessel diameters were also correlated with gestational age.
Conclusion : First trimester umbilical cord and vessel diameters of Thai fetuses are related to gestational age. The presented reference ranges might be useful for further studies, such as prediction of adverse pregnancy outcome or combination with biochemical or other ultrasound markers for fetal aneuploidy
screening.

Keywords : Diameter, Umbilical cord, Umbilical vessels, First trimester, Thai fetuses