Transvaginal sonography for fetal crown-rump length measurement in a Thai population.

ABSTRACT

A prospective descriptive cross-sectional study was undertaken at the Department of Obstetrics and Gynecology, Faculty of Medicine, Chulalongkorn University to establish a reference interval for fetal crown-rump length (CRL) in a Thai population using transvaginal ultrasound. This study was performed on normal pregnant women registered at the antenatal clinic in their first trimester. All had a good menstrual history. CRL measurement was obtained by a 5 MHz vaginal probe. All of the newborns were proved to be normal at birth. We constructed and compared CRL (mm) relating to gestational age (GA) (days). Five hundred and forty seven cases were enrolled into the study. CRL was correlated with gestational age. The best fit regression equation was the quadratic model CRL (mm) = -13.872 - 0.014 GA (day) + 0.0097 GA (day)2, R = 0.92, p < 0.0001). Centiles and a chart for CRL derived from the regression equation are presented. In conclusion, a reference interval for fetal crown-rump length in a Thai population has been established. This data may be useful in the early detection of genetic or environmental disorders affecting fetal growth in the first trimester of pregnancy.