Charts of Thai Fetal Biometries: 1. Methodology
DITTAKARN BORIBOONHIRUNSARN, M.D., M.P.H.*,
PRASERT SUNSANEEVITHA Y AKUL, M.D.*,
WIBOOLPHAN THIT ADILOK, M.D.*,
VITTAYA TITAPANT, M.D.*,
TEERA SIWADUNE, M.D.**,
PORNPIMOL RUANGVUTILERT, M.D.*
Affiliation : *Department of Obstetrics and Gynecology, Faculty of Medicine Siriraj Hospital, Mahidol University. Bangkok
10700,
** Division of Obstetrics, Chon Buri Hospital, Chon Buri 20000, Thailand.
AbstractA cross-sectiooal study was conducted in order to construct new reference charts for
Thai fetal biometries that are commonly used in obstetric ultrasound practice. We discussed and
illustrated a sound appropriate study design and statistical analysis which lead to more valid
results. A total of 621 normal pregnant women between 12-41 weeks of gestation and their
fetuses were recruited. Each fetus was measured once at a randomly assigned gestational age
specifically for the purpose of this study only. Stepwise linear regression technique was used to
model the mean and its standard deviation as functions of gestational age. Goodness of fit and
normality of the data were checked before the final models were chosen. Reference centiles
were derived, taking into account the increasing variation as pregnancy proceeds. We demon-
strated the stated technique with humerus data from the same study. Reference charts for
other fetal biometries have been derived and are presented in subsequent papers.
Keywords : Fetal Biometries, Methodology, Reference Centiles
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