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A cross-sectional study was conducted in order to construct a new reference chart for Thai fetal abdominal circumference (AC). A total of 621 normal pregnant women between 12-41 weeks of gestation and their fetuses were recruited. Measurements were made once at a randomly assigned gestational age specifically for the purpose of this study only. Due to unfavorable fetal position in some cases, AC data were available in 615 measurements. Linear regression models were fitted separately to estimate the mean and standard deviation as functions of gestational age. Reference centiles were constructed from both equations, assuming the data were normally distributed. A new reference centiles for AC is presented and compared with previously published data. Our derived centiles were lower than those from Western studies which may partly be due to racial differences. This emphasizes the need to develop fetal biometries charts specifically for each region.

A cross-sectional study was conducted in order to construct a new reference chart for Thai fetal femur length (FL). A total of 621 normal pregnant women between 12-41 weeks of gestation and their fetuses were enrolled. Measurements were made once at a randomly assigned gestational age specifically for the purpose of this study only. Femur length data were available in 608 measurements due to unfavorable fetal position in some cases. Linear regression technique was used to model separately the mean and standard deviation as functions of gestational age. Reference centiles were constructed from a combination of both models, assuming the data were normally distributed. A new reference centiles chart for FL is presented and compared with previously published data. While our derived centiles were clearly lower than those from Western studies, they were found comparable with those from a Thai study. This demonstrated the important effect of racial differences between populations on fetal biometries and elucidates the need to develop fetal biometries charts specifically for each region.

A cross-sectional 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 demonstrated 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.

A cross-sectional study was conducted in order to construct a new reference chart for Thai fetal biparietal diameter (BPD). A total of 621 normal pregnant women between 12-41 weeks of gestation and their fetuses were recruited. Measurements were made once at a randomly assigned gestational age specifically for the purpose of this study only. Due to unfavorable fetal position in some cases, BPD data were available in 613 measurements. Linear regression models were fitted separately to estimate the mean and standard deviation as functions of gestational age. Reference centiles were constructed from both equations, assuming the data were normally distributed. A new reference centiles chart for BPD is presented and compared with previously published data. Our derived centiles were clearly lower than those from Western studies showing the importance of racial differences between populations. This elucidates the need to develop fetal biometries charts specifically for each region.