Transvaginal Sonography for Fetal Crown-Rump
Length Measurement in a Thai Population
YUEN TANNIRANDORN, M.D.*, SAKNAN MANOTAYA,M.D.*,
BOONCHAI UERPAIROJKIT, M.D.*, SOMCHAI TANAWATTANACHAROEN,M.D.*,
TEERA WACHARAPRECHANONT, M.D.*, DHIRAPHONGS CHAROENVIDHYA , M.D.*
Affiliation : *Department of Obstetrics and Gynecology, Faculty of Medicine, Chulalongkorn University, Bangkok, 10330, Thailand.
AbstractA 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 com
pared 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.
Keywords : Reference Interval, Crown-Rump Length, Transvaginal Ultrasound, First Trimester
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