Sk Park

Estimation of fetal weight with the use of head, body, and femur measurements—A prospective study

In utero estimates of fetal weight were evaluated prospectively in 109 fetuses with the use of sonographic models developed in a previous study. This report confirms that the best in utero weight estimates result from the use of models based on measurements of head size, abdominal size, and femur length. Since the accuracy of these models (1 SD = 7.5%) is significantly better than those based on measurements of head and body (e.g., biparietal diameter, abdominal circumference), we recommend routine use of such models in obstetric sonography.

Fetal biparietal diameter: a critical re-evaluation of the relation to menstrual age by means of real-time ultrasound.

The relationship between fetal biparietal diameter (BPD) and menstrual age was determined by cross‐sectional analysis of 533 fetuses (12 to 40 weeks) examined with a linear array real‐time (dynamic image) scanner using specifically defined methodology. Mathematical modeling of the data demonstrated that the optimal fit was the linear cubic function (r2 = 99 per cent); predicted BPD values calculated from the function were most comparable with composite data from cross‐sectional studies performed with static scanners after 1974 (average difference, 0.22 mm) and least comparable with composite data from cross‐sectional studies performed with static scanners before 1974 (average difference, 2.0 mm). The variability associated with predicting menstrual age from the BPD increased progressively throughout gestation; the maximal variability was noted between 36 and 42 weeks (+/‐ 3.6 weeks). Comparison with our longitudinal study of BPD growth indicates that the cross‐sectional data represent a valid estimate of the true longitudinal BPD growth curve of the population.

Estimating fetal age using multiple parameters: A prospective evaluation in a racially mixed population

This study was designed to evaluate the accuracy of regression models for menstrual age prediction using single versus multiple fetal ultrasonographic measurements (biparietal diameter, head circumference, abdominal circumference, and femur length). The models tested had been previously developed from a study of middle-class white patients in a private hospital. The current study population consisted of 300 indigent black and Hispanic patients seen in a county hospital. This study demonstrated prospectively that the use of multiple parameters in estimating fetal age offers a significant advantage over any single parameter used alone and that the regression equations developed from a middle-class white population appear to be applicable to fetuses from a population with different socioeconomic and racial characteristics.

An evaluation of two methods for measuring fetal head and body circumferences.

Head and abdominal circumference measurements of 166 fetuses (15‐40 weeks) were made by three different examiners using two measurement techniques. In method 1 the actual circumferences were measured using an electronic digitizer, while in method 2 the circumference measurements were estimated using the formula for calculating the circumference for an ellipse. Evaluation of the entire data set as a whole demonstrated no significant mean errors (P > 0.05), and only a small degree of variability (2 SD = 6 per cent). Evaluation of the data for each examiner demonstrated no significant differences (P > 0.05) in the observed variability, but small statistically significant mean errors (1.7‐4.1 per cent) were observed. The latter finding is thought not to be a limitation of the ellipse approximation technique, since similar findings have been observed when experienced sonographers make actual circumference measurements on the same fetus using the same equipment.

Relation of fetal femur length to neonatal crown-heel length.

Sonographically measured femur lengths in 102 fetuses were compared with neonatal crown‐heel lengths within 72 hours of delivery. The optimal model for describing crown‐heel length as a function of femur length was a linear model, with a coefficient of determination (r2) of 66 per cent; the standard deviation in predicting crown‐heel length from femur length was 2.4 cm. These data were compared with autopsy data from the literature, which showed an even stronger correlation between femur length and crown‐heel length. Because of the strong correlation between these two dimensions, the femur length should prove useful in the detection of intrauterine growth retardation when crown‐heel length is compromised. It should also be useful as a variable in the prediction of fetal weight in utero, since crown‐heel lengths at the extremes of normal can significantly affect in utero weight estimates using ultrasound.

Sonographic fetal growth standards. Are current data applicable to a racially mixed population

Currently available sonographic growth standards for fetal head size, abdominal size, and limb length are based primarily on studies from white populations. To determine whether these published standards are appropriate for a racially mixed, indigent population, we compared our published data from a middle‐class white population with data generated from a black/Hispanic population seen at a county hospital in Houston, Texas. No statistically significant differences were found for any of the following fetal sonographic parameters (20 to 41 weeks): biparietal diameter, head circumference, abdominal circumference, femur length.