Transvaginal fetal biometry in early pregnancy.

Abstract

To produce reference charts for fetal size with transvaginal sonography that are potentially helpful in evaluating normal and abnormal early pregnancies. A prospective cross-sectional study. 1081 normal singleton pregnancies with a normal fetal karyotype or normal healthy baby at delivery, at 9-16 weeks' gestation. Measurements included crown rump length, biparietal diameter, transverse cerebellar diameter, head and abdominal circumference, mean abdominal diameter, thoracic circumference, femur length, humerus length and foot length. The best description of the relationship between single ultrasonographic parameters and gestational age was achieved by polynomial regression analysis. All fetal biometric parameters correlated closely with gestational age. Biparietal diameter maintained the closest correlation with gestational age (r2 = 97.15, p < 0.001; y = -0.545 - 0.06x + 0.15x2); transverse cerebellar diameter showed the poorest correlation with gestational age (r2 = 88.17, p < 0.001). Reference ranges (5 degrees and 95 degrees percentile intervals) were constructed for all biometric parameters in relation to gestational age. Mean residuals are similar for all parameters with a very low range. These data provide normograms for first and early second trimester fetal measurements which may be of aid in the dating of pregnancies and can be useful in the early detection of genetic disorders affecting the growth of fetal structures.