Fetal weight estimation by real-time ultrasound measurement of biparietal and transverse trunk diameter

Ultrasonographic fetal weight estimation by an integrated computer-assisted system: can each laboratory improve its accuracy?

Estimated fetal weights from 1684 cases with singleton, live infants born within 7 days of an ultrasonographic examinations were compared with their birth weights, which ranged from 520 to 5920 gm. Estimated weight calculated from Shepard's equation produced a linear relationship of birth weight against estimated weight with an intercept and slope of 209.5 gm and 0.929. Overall, 75% of the estimated weights were within 15% of the actual weight. A separate regression model that used the same variables from Shepard's equation failed to improve the comparison between estimated and actual weights. All cases were reevaluated with multiple regression modeling. Various examination-to-birth intervals were analyzed; intervals less than or equal to 3 days appeared optimal. The best equation increased the percent of cases that were within 15% of the actual birth weight to 80%. The plot of birth weight against estimated weight had an intercept and slope of 33.1 gm and 0.994. Unlike Shepard's equation, the best equation was not statistically different from the ideal one-to-one relationship between estimated and actual weight. When the new equation was applied to an additional 339 new cases, equally accurate results were obtained. Customizing a laboratory's ultrasonographic weight estimation equations may be necessary to obtain the best estimate of fetal weight.

Sonographically estimated fetal weights: accuracy and limitation

To determine the accuracy of our ultrasonographically predicted birth weights we studied 1301 women delivered of infants within a week of an obstetric ultrasonogram to compare the ultrasonographically predicted birth weights with the actual birth weights. The fetuses varied from 700 to 5800 gm and were consecutive singleton fetuses in vertex presentations delivered at a single institution. Overall 74% of the infants had birth weights within 10% of the ultrasonographic estimates and 42% had birth weights within 5% of the ultrasonographic estimates. The presence of oligohydramnios or polyhydramnios made no difference in the percent errors. The sensitivity for identifying a fetus with macrosomia (birth weight greater than 4000 gm) with an estimated weight of greater than or equal to 4000 gm was 65%. The specificity or percent of fetuses correctly identified ultrasonographically as not macrosomic was 90%. If fetuses predicted by ultrasonography to be greater than 3800 gm were included, the sensitivity for the prediction of macrosomia rises to 82% but the specificity would be 79%. There appears to be a fixed limitation to obtaining estimated fetal weights by ultrasonography, even in large series, because these data reaffirm the success and limitations of other methods used to estimate fetal weight previously reported in the literature.

Estimation of fetal weight in the third trimester by ultrasound

A method to estimate the intrauterine fetal weight by use of ultrasound measurements of the fetal biparietal diameter (BPD) and the abdominal diameter (AD) is presented. From a consecutive series of single pregnancies the 238 pregnancies (3% of the hospital population) with ultrasound measurements obtained within 4 days before delivery were used in the estimation of birth weight. In addition, the estimated formula was applied on a test material consisting of 100 similarly selected pregnancies from the same hospital. To evaluate the expected selection effects, the birth weight for gestational age in the study group was compared with birth weight for gestational age in the total population. The weight could be estimated as 0.0351 X AD1.65 X BPD0.69 X exp(0.00196 X gestational age). Thus, the actual birth weight was within 83-120% of the estimated weight (95% prediction limits), with a residual coefficient of variation of about 9%. The gestational age could be omitted without major influence on the weight prediction. When applying the formula on the test material, 70% of the actual weights deviated less than 10% from the estimated fetal weight, but a tendency towards a slight overestimation of the weight for light for gestational age infants was found.

Maternal serum alpha-fetoprotein in twin pregnancies uncomplicated by neural tube defect

The maternal serum alpha-fetoprotein concentration was measured between 16 and 20 weeks in 145 twin pregnancies in which neither fetus had a neural tube defect. When the maternal serum alpha-fetoprotein concentration was less than two multiples of the singleton median, pregnancy outcome was good; the extended perinatal mortality rate was 32.6/1000, mean birth weights for the first and second twins were 2507 and 2443 gm, respectively, and mean gestation at delivery was 36 weeks, 6 days. When the maternal serum alpha-fetoprotein concentration was greater than four multiples of the singleton median, the outcome was poor; the extended perinatal mortality was 400/1000, mean birth weights were 1963 and 1523 gm, and mean gestation at delivery was 32 weeks, 4 days. The negative correlations of maternal serum alpha-fetoprotein concentration with birth weight and gestation at delivery were highly significant. Maternal serum alpha-fetoprotein concentration in midpregnancy is a useful predictor of outcome in twin pregnancy, independent of the occurrence of neural tube defect, and it appears to be related to the timing of delivery rather than fetal growth.

Use of ultrasound in antenatal diagnosis of large-for-gestational age infants in diabetic gravid patients

Near-term ultrasonograms of 44 diabetic gravid patients and 47 nondiabetic gravid patients were retrospectively analyzed. The mean values of abdominal diameter to femur length ratios and abdominal diameter to biparietal diameter ratios in diabetic gravid patients with large-for-gestational age fetuses were significantly different from those values in diabetic patients with appropriate-for-gestational age fetuses and in nondiabetic patients. Glycosylated hemoglobin values were above 7.4% (mean +/- 2 SD) in 79% of diabetic patients with large-for-gestational age infants and abdominal diameter to femur length ratio exceeding 1.385. Glycosylated hemoglobin values were less than or equal to 7.4% in 69% of diabetic gravid patients with appropriate-for-gestational age fetuses and abdominal diameter to femur length ratio less than 1.385. These findings suggest that large-for-gestational age infants have a different growth characteristic with a disproportionate enlargement of the abdomen. This possibly results from a long period of elevated levels of maternal plasma glucose (as shown by elevated values of glycosylated hemoglobin).

Ultrasonic fetal weight estimation in multiple and singleton pregnancy

Thirty-five multiple and 168 singleton fetal weight estimations were made in an Australian population using the tables of Warsof et al., which have been computed from a North American population. The estimated fetal weights were compared to the actual birth weights within 96 h of estimation. Correlation coefficients of the actual birth weight with the estimated fetal weight for the total group, singleton and multiple pregnancies respectively, were 0.967, 0.969 and 0.933. The percentages of estimated fetal weights falling within 10% of the actual birth weight were for the three groups, 79.3%, 77.9% and 85.7% respectively. Individual weight sub-groups, less than 1500 g, 1500-2500 g, 2500-4000 g and greater than 4000 g, showed correlation coefficients of 0.84, 0.838, 0.839 and 0.759 respectively, which compare favourably to published studies of North American populations using this method. It is concluded that ultrasonic fetal weight estimation using the North American computerized tables of Warsof et al. is appropriate for an Australian population and is valid for both singleton and multiple pregnancies.