Sonographic femur length/abdominal circumference ratio in normal pregnancies among Thais.

The relationship between sonographically measured foetal length (FL) and abdominal circumference (AC) (expressed as FL/AC ratio * 100) was studied in 455 normal pregnancies between the 14th and 40th gestational weeks. By analysis of 1,197 measurements for each parameter, this ratio was found to be independent of menstrual age, with a normal range after 21 weeks (mean + 2 S.D.) of 2038 + 2.6. This mean ratio is different from the values of a previous western study (22+2). The ratio obtained from the Thai study hopefully will be the baseline for the Thai population and may be used for further study about intrauterine growth retardation.