Estimation of birth weight by use of ultrasonographic formulas targeted to large-, appropriate-, and small-for-gestational-age fetuses

Utilizing sonography to follow fetal growth

In utero diagnosis of fetal growth abnormalities continues to pose a clinical dilemma. Although significant advances have been made in the understanding of growth disturbances and their clinical importance, false-positive and false-negative diagnoses of IUGR and excessive fetal growth continue to affect the accuracy of antenatal diagnosis. Until more accurate methods are developed to aid in diagnosis, multiple biometric parameters should be assessed in patients either at risk for or with a suspected growth disturbance. Serial measurements obtained every 2 to 3 weeks may enhance diagnostic capabilities. Although antenatal diagnosis of IUGR has been shown to be of benefit in improving outcome, more study is needed to determine whether there is a benefit in antenatal diagnosis of macrosomia or LGA.

Prediction of birth weight using the Rossavik growth model: a study in a Dutch population

OBJECTIVES

To evaluate the Rossavik growth model for predicting birth weight in a Dutch population and to evaluate growth cessation near term.

STUDY DESIGN

Birth weight was predicted at various ages between 38 and 42 weeks, menstrual age (MA), and at birth age in 50 normal infants using two sets of ultrasound measurements obtained before 28 weeks, MA. Predicted birth weights were compared to actual weights. The mean percentage difference was used as a measure of systematic error and the standard deviation as a measure of random error. Linear regression analysis was used to evaluate the relationship between percentage differences and birth age. To evaluate the individual growth potential, the Growth Potential Realization Index for weight (GPRIWT) was determined for each fetus.

RESULTS

The predictions at 39 and 39.15 weeks, MA, were accurate without systematic error and with a random error of +/-9.3%. Prediction at 38 weeks showed a statistical underestimation (mean +/- SD = -5.8% +/- 8.8), and statistical overestimations were found for predictions after 39.15 weeks and at birth age. A relationship between percentage differences and birth age was not found for predictions between 39.15 and 40 weeks, MA. These findings indicate that growth cessation occurred at 39.15 weeks, MA. Using birth weights predicted at 39.15 weeks, MA, GPRIWT were calculated. The mean GPRIWT value was not significantly different from 100% (p > 0.05), and individual GPRIWT values ranged from 84% to 114%.

CONCLUSIONS

The Rossavik growth model can be used to predict birth weight in a Dutch population. However, growth cessation near term appears to occur later than previously reported in other populations.

Fetal distress due to placental insufficiency at 26 through 31 weeks: a comparison between an active and a more conservative management

OBJECTIVE

To compare perinatal mortality and short-term morbidity in extremely preterm infants with fetal distress due to placental insufficiency in two centers with different management attitude.

DESIGN

Retrospective cohort study in two university hospitals of all infants with fetal growth retardation due to placental insufficiency resulting in signs of fetal distress at 26 through 31 weeks gestational age, during the years 1984 through 1989. Center A followed a conservative management: in some cases the risk of major handicaps or mortality was estimated so high, based on antenatally estimated fetal weight and gestational age, that the decision was taken to abstain from treatment. In all other cases cesarean section took place, but only if fetal distress was obvious. Center B used a more active management: cesarean section was performed in all cases, sometimes with only minor changes in fetal heart rate variability.

RESULTS

Overall survival differed significantly: 55% (center A) versus 72% (center B), largely due to antenatal mortality in center A. Discharge survival rate of liveborn infants was 81% in center A and 72% in center B. More than half of the postnatal mortality was attributed to respiratory causes in both centres. An active management showed a tendency to a higher incidence of short-term morbidity.

CONCLUSION

Selection by antenatal prediction of postnatal mortality using estimated fetal weight fails. Even in the group with the lowest birthweight postnatal mortality did not surpass 50%. Early intervention may be associated with higher short-term morbidity. Long-term follow-up of these children is needed to discriminate between both policies with regard to further development of surviving infants.

Clinical and ultrasound prediction of macrosomia in diabetic pregnancy

OBJECTIVE

To study prospectively the prediction power, at different gestations, of clinical and ultrasound measurements for fetal size in diabetic pregnancy.

SETTING

A large combined obstetric diabetic clinic in a teaching hospital.

PARTICIPANTS

One hundred and eighty-one pregnancies in which women had scans at least two of three specific time points and who were delivered of singletons after 34 weeks: 73% were pre-gestational insulin-dependent diabetics, the others were pre-gestational White class A or gestational diabetics.

INTERVENTIONS

Clinical estimates of fundal height and fetal size and ultrasound estimates of abdominal circumference and head circumference were routinely carried out at gestational ages of 28, 34 and 38 weeks or before delivery.

MAIN OUTCOME MEASURES

Standardised birthweight, corrected for gestation and parity. The relation with clinical and ultrasound measurements was investigated using multiple linear regression and the capability of the measurements to predict macrosomic births (> 95th centile of normals) using receiver-operator characteristic curves.

RESULTS

All measurements are poor predictors of eventual standardised birthweight. Prediction improves with closeness to delivery. Prediction is significantly improved by adding ultrasound to clinical information, but at 34 weeks or later this only contributes 8% of the variance. There is no difference in the prediction power for macrosomia between clinical and ultrasound measurements.

CONCLUSIONS

Even regular serial scanning and clinical examination will not always diagnose the macrosomic fetus in diabetic pregnancy. In our hands, clinical examination is as predictive as ultrasound measurements. Ultrasound does add to clinical prediction power but only to a small extent. Ultrasound should be used in a selected way, as defined by clinical findings, and with recognition and understanding of the errors and biases involved.

Pregnancy-specific beta 1-glycoprotein (SP1) and its relation to fetal birth weight at term pregnancy

The relation between serum levels of pregnancy-specific beta 1-glycoprotein (SP1) and actual fetal and placental weights was studied in 100 full-term pregnant women. This was compared with fetal weight determination by ultrasound. SP1 levels significantly correlated with fetal and placental weights. Its determination was found to be comparable to ultrasonography in placental fetal weight assessment, especially at the extremes of fetal weight (macrosomia and small for gestational age) where special obstetric management is warranted.

Fetal growth disturbances

IUGR is a fetal disorder characterized by diminished fetal growth, especially in the third trimester. Growth retardation may be due to primary placental insufficiency or may result from a variety of maternal or fetal causes and is associated with elevated perinatal mortality and morbidity. Numerous conventional and Doppler ultrasound criteria have been proposed for diagnosing IUGR prenatally, but none on its own permits confident diagnosis of this condition. Diagnosis or exclusion of IUGR can best be achieved by the combined use of three parameters: estimated fetal weight, amniotic fluid volume, and maternal hypertension. When IUGR is suspected based on these parameters, Doppler ultrasound can help to determine the prognosis. Large fetuses, particularly those weighing more than 4,000 grams at birth, are at risk for perinatal morbidity and mortality due to obstetrical complications. These fetuses occur more frequently and are at especially high risk in diabetic mothers. The estimated fetal weight is the most direct parameter for diagnosing LGA and macrosomia and is moderately accurate with positive predictive values up to 67% in the general population and 77% in diabetics. It can be an important factor in deciding on the route of delivery in diabetic mothers.

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.

Multiple pregnancy: an international perspective

This article discusses the following areas of interest related to the obstetric care of multiple pregnancy: 1) methods of diagnosis and ultrasound, 2) pregnancy protection through adequate maternal nutrition, 3) mode of delivery, 4) discordant twins, and 5) assisted reproductive technology. The article also emphasizes the FIGO/WHO concerns regarding safe motherhood and proposes a four point program to reduce perinatal death rates in multiple pregnancy. These elements are: 1) adequate primary health care including access to family planning information and technology, 2) prenatal care with referral of high risk patients to specialized centers, 3) the presence of trained personnel for all women in childbirth, 4) effective access to obstetric care for women who are pregnant, giving birth, or recently delivered.