Transvaginal sonography for fetal measurement in early pregnancy

To establish reference ranges for fetal size by gestation in the first trimester as indicated by cephalic, abdominal and limb measurements using transvaginal sonography. Design. A prospective descriptive study. Setting. Two antenatal clinics in Milan, Italy. Subjects. 270 women with normal singleton pregnancies at 42-108 days gestation. All had regular cycles and certain dates. Interventions. Vaginal ultrasound examination including inspection of fetal structures and lasting 5-15 min. Main outcome measures. As many of the following fetal measurements as possible according to gestational age and ease: crown-rump length (CRL), biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur and foot lengths. Results. CRL was measured in 183 fetuses, BPD in 201, HC in 162, AC in 160, femur length in 133 and foot length in 62. The best description of the relation of CRL to gestational age was achieved by a quadratic function (y = -3.98 - 0.308x + 0.0117 x²). Mean values thus derived were virtually identical to those obtained by Robinson and Fleming in 1975 with transabdominal static scanning. Fetal BPD, HC, AC and femur length correlated more closely with CRL than gestational age. Reference ranges (mean and 95% data intervals) were constructed for each biometrical measurement in relation to gestational age and CRL. The HC/AC and femur/foot length ratios did not show any significant variation with gestational age or CRL. Conclusions. These data may be useful in the early detection of genetic disorders affecting the growth of fetal had, trunk and limbs. Genetic and/or environmental variables play an appreciable role in the modulation of early fetal growth.