Frank P. Hadlock

Use of ultrasound in the detection of macrosomia: a review

The early detection af the macrosomic fetus is important to the obstetric management of pregnancies in which this growth abnormality occurs. Ultrasound has been used for this purpose but for this approach to be effective, a clear definition of macrosomia, selection of the appropriate parameters for measurement and specification of the optimal time for carrying out the ultrasound studies are required. In this review we examine the definition of macrosomia and introduce two new terms, mechanical macrosomia and metabolic macrosomia. We also evaluate the effectiveness of the limited number of parameters studied to date and conclude that they are marginally effective, primarily because of their low sensitivity and the limitations of current ultrasound methods for estimating fetal weight. The use of the growth profile, a multiparameter approach to the evaluation of fetal growth, is suggested as a possible means for improving the effectiveness of ultrasound in detecting the macrosomic fetus.

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.

The femur length/head circumference relation in obstetric sonography.

The relationship of sonographic femur length to biparietal diameter (BPD) in utero may be useful in detecting short‐limb dwarfism, hydrocephaly, microcephaly, and measurement errors. Because BPD can be adversely affected by head shape changes (e.g., dolichocephaly), falsely high or low values of femur length/BPD could result. Because head circumference is less affected by head shape changes than is BPD, it should be a better standard of head size against which to judge limb length. The authors report normal values for the relationship between femur length and head circumference, based on a cross‐sectional analysis of 361 normal fetuses (15‐42 weeks) using real‐time ultrasound.

Fetal body ratios in second trimester: a useful tool for identifying chromosomal abnormalities?

This study was carried out to determine if second trimester fetal body ratios are useful in detecting chromosomally abnormal fetuses. As a reference population, normative data for five fetal body ratios (femur length/biparietal diameter, biparietal diameter/fetal length, femur length/head circumference, head circumference/abdominal circumference, and femur length/abdominal circumference) were derived using regression analysis from a population of chromosomally normal fetuses (n = 1770) who underwent genetic amniocentesis at our institution between 14 and 21 menstrual weeks. During the same time period, 37 chromosomally abnormal fetuses were identified by amniocentesis. In comparing the two groups using the 10th and 90th percentiles as cutoffs between normal and abnormal, approximately 25% of chromosomally abnormal fetuses were identified, whereas approximately 20% of the normal fetuses were incorrectly classified as abnormal. Moreover, the use of 1.5 standard deviations above the mean for BPD/FL identified only 19% of Down syndrome fetuses. Our data, and those from a comprehensive review of the literature, suggest that the sensitivity of these ratios in detecting chromosomally abnormal fetuses is too low to recommend them for routine screening.