An evaluation of two equations for predicting fetal weight by ultrasound

The relationship between umbilical artery Doppler velocimetry and fetal biometry

The relationship between peak-systolic/end-diastolic ratio of the umbilical artery waveform and fetal biometry was studied in 127 uncomplicated pregnancies with established dates between 20 and 40 weeks' gestation. At each ultrasonographic examination fetal biometry included measurement of the biparietal diameter, head circumference, abdominal circumference, and femur length. The peak-systolic/end-diastolic ratio was measured by either a continuous or a pulsed-wave method. There were significant linear negative correlations between all the biometric parameters, as well as between the ultrasonographically estimated fetal weight and peak-systolic/end-diastolic ratio. Of the individual ultrasonographic parameters the femur length (for gestations less than 30 weeks) and the abdominal circumference (for gestations greater than or equal to 30 weeks) were found to be best correlated with the peak-systolic/end-diastolic ratio. Regression curves, including the 10th and the 90th percentile, were developed between each biometric parameter (biparietal diameter, head circumference, abdominal circumference, and femur length), as well as between estimated fetal weight and peak-systolic/end-diastolic ratio. The estimated fetal weight nomogram had the best sensitivity (48%) in predicting intrauterine growth retardation. These nomograms should prove most useful in assessing downstream placental vascular resistance in high-risk patients with unknown dates.

Does amniotic fluid index affect the accuracy of estimated fetal weight in preterm premature rupture of membranes?

Estimated fetal weights play a critical role in the management scheme of patients with preterm premature rupture of membranes but are often technically difficult to obtain in these patients because of low amniotic fluid volume. Previous studies have had conflicting data as to the accuracy of estimated fetal weights in preterm premature rupture of membranes. This study was undertaken to evaluate the effect of amniotic fluid index on the accuracy of estimated fetal weights in pregnancies complicated by preterm premature rupture of membranes. Over a 2-year period at Long Beach Memorial Medical Center, 98 patients with preterm premature rupture of membranes who had an ultrasonographic examination with estimated fetal weights and amniotic fluid index performed within 48 hours of delivery were identified and compared with a control group of 55 patients in preterm labor with normal amniotic fluid index for gestational age, also obtained within 48 hours of delivery. Shepard and Hadlock formulas were used to estimate fetal weight. Results were measured in percent error from the actual birth weight. All birth weights were less than 2000 gm. No statistical differences were identified. The value of amniotic fluid index did not affect the accuracy of predicted estimated fetal weight in preterm premature rupture of membranes. Predicted estimated fetal weight of patients with preterm premature rupture of membranes appears to be as accurate as predicted estimated fetal weight in pregnancies with normal amniotic fluid volumes.

Intrapartum ultrasonographic estimates of fetal weight by the house staff

In spite of the widespread use of ultrasonographic estimates of fetal weight, a paucity of data exists with regard to its use in patients who are in labor. The purpose of this study was to evaluate the accuracy of ultrasonographic estimates of fetal weight in a busy labor and delivery suite by the house staff. Measurements of biparietal diameter, abdominal circumference, and femur length were prospectively obtained in 109 patients in labor in whom this information was expected to be contributory in making delivery plans. All patients were delivered within 48 hours of ultrasonographic evaluation. Measurements of abdominal circumference were obtained in all cases. Biparietal diameter and femur length were obtained in 85% and 92% of cases, respectively. Overall, the mean absolute errors were 9.3% and 9.2% for estimated fetal weight by biparietal diameter/abdominal circumference and abdominal circumference/femur length ratios, respectively. Estimated fetal weight by biparietal/diameter/abdominal circumference ratio was not significantly different from that by femur length/abdominal circumference ratio. In conclusion, the accuracy of intrapartum estimates of fetal weight performed by the house staff in a busy labor and delivery unit is comparable to that reported for estimates obtained during the antepartum period by professional users of ultrasonography in a controlled setting.

The fetal-pelvic index: a method of identifying fetal-pelvic disproportion in women attempting vaginal birth after previous cesarean delivery

In 1986 the fetal-pelvic index was introduced as an accurate method of prospectively identifying the presence or absence of fetal-pelvic disproportion. The concept of the fetal-pelvic index is one in which the fetal head and abdominal circumferences (ultrasonographic mensuration) are compared with the respective maternal pelvic inlet and midpelvic circumferences (x-ray pelvimetry). The purpose of this study is to evaluate the efficacy of this index as a predictor of fetal-pelvic disproportion in gravid women attempting vaginal birth after previous cesarean delivery. Findings of the fetal-pelvic index are compared with those of two other means of identifying fetal-pelvic disproportion (Colcher-Sussman x-ray pelvimetry and ultrasonographically derived estimated fetal weight of greater than or equal to 4000 gm). Of the 65 prospective study participants, 18 (28%) failed to progress in labor, and a repeat cesarean delivery was required. Forty-seven of the 52 patients with a negative fetal-pelvic index value were delivered vaginally (negative predictability = 0.90). Of the five with false-negative fetal-pelvic index values, four fetuses persisted in an occipitoposterior position and failed to progress in labor. All 13 patients with a positive fetal-pelvic index value failed to progress in labor and required a cesarean delivery (positive predictability = 1.00). In contrast, when used alone, neither x-ray pelvimetry nor ultrasonography-determined estimated fetal weight of greater than or equal to 4000 gm provided accurate identification of fetal-pelvic disproportion.

The effect of maternal height on birth weight and birth length

This retrospective study examined the gestational age at which differences were observed between birth weights and birth lengths of infants whose mothers differed by height. Infants whose gestational ages were between 24 and 42 weeks born to women 59-62 inches (150-157 cm) tall were compared to similar infants born to women 66-69 inches (168-175 cm) tall. Significant differences occurred in birth weight and birth length from 35 weeks onward. The infants of the shorter women were symmetrically smaller than the infants of the taller women as the infant ponderal indexes did not differ.

Assessment of fetal well-being with magnetic resonance

The application of magnetic resonance techniques in the assessment of fetal growth, fetal growth patterns and fetal health was assessed. Eighty-four sets of fetal images were obtained using a fast-scan magnetic resonance imaging technique. Measurements were made of fetal subcutaneous fat thickness, uterine cavity length and width, fetal and uterine cross-sectional areas and fetal volume. Fetal area and fetal volume measurements were found to correlate well with birth weight. Measurement of subcutaneous fat thickness may prove to be a means of differentiating between those fetuses who are constitutionally as opposed to pathologically large or small. Thirteen women had additional spectroscopic studies carried out. Twelve of the women had normal pregnancies. One woman had a twin pregnancy in which one twin died. 31P phosphorus spectra were obtained from seven of the normal pregnancies. In the remainder, the depth of the abdominal wall prevented spectra being obtained from the placenta. Differences in phosphorus metabolites were obtained from the placenta of the dead twin compared to those from the healthy pregnancies.

Reliability of ultrasonographic formulary in the prediction of fetal weight and survival of very-low-birth-weight infants

Antenatal management of very-low-birth-weight infants often requires difficult obstetric decisions. This study was designed to evaluate the predictive value for neonatal outcome of antenatally acquired estimation of gestational age and ultrasonographically estimated fetal weight or a combination of both in very-low-birth-weight infants. Sixty-seven fetuses with estimated gestational ages between 22 0/7 and 28 6/7 weeks were studied ultrasonographically to estimate fetal weight. A comparison of accuracy of estimated fetal weight with actual birth weight showed good correlation (r = 0.93). Neonatal outcome of these infants was analyzed by estimated gestational age and estimated fetal weight. Estimated gestational age and estimated fetal weight greater than 25 weeks and greater than 750 gm were associated with 50% survival, respectively. However, when both of these conditions were met survival reached 85%. This information may be useful to guide antepartum management decisions in this very-low-birth-weight group.

Effects of intravascular fetal blood transfusion on fetal intracardiac Doppler velocity waveforms

In 12 fetuses from pregnancies with red blood cell isoimmunization Doppler velocity waveforms were recorded at the level of atrioventricular valves immediately before and at 15-minute intervals for 2 hours after the intravascular transfusion. The left and right cardiac outputs, the ratio between the peak velocities during early passive ventricular filling and active atrial filling at the level of both ventricles as well as the heart rate were calculated. Before transfusion, the left and right cardiac outputs were significantly higher than reference ranges for gestation that were constructed from the cross-sectional study of 187 normal pregnancies. After transfusion there was a significant temporary fall in right and left outputs associated with increased ratios between the peak velocities during early passive ventricular filling and active atrial filling. Within 2 hours after transfusion both parameters returned toward the normal range. In addition, no significant changes were found for fetal heart rate values before and after transfusion. The fall of cardiac output was significantly related to the amount of expansion of the feto-placental volume.

Normal fetal growth evaluated by longitudinal ultrasound examinations

Fetal weight estimation was evaluated using the equations of Warsof, Shepard and Hadlock in 192 patients, less than 3 days before delivery. Warsof's and Hadlock's equations resulted in significantly better weight estimates compared to Shepard's equation. No systematic error was found below 2500 g by use of Warsof's equation, whereas Shepard's and Hadlocks's equations resulted in significant over-estimation in the low weight group. In a study of 5 fetuses, of 27-38 weeks gestational age, the intra-observer variation was calculated to 4.6%, whereas the coefficient of variation among observer means was 2.9%. The mixed intra- and inter-observer coefficient of variation was 6.5%. Thirty-five low-risk, uncomplicated pregnancies with reliable last menstrual dates were investigated longitudinally with ultrasound measurements of fetal weight. Population growth curves of fetal weight, fetal femur length, abdominal circumference and biparietal diameter were constructed by weighted polynomial regression. After 27 weeks of gestational age the weight growth curve showed only insignificant non-linearity. Compared to a Danish growth curve based on birth weights, significant higher mean weight was found, especially before 31 weeks of gestational age. The 10th and 90th percentiles for the individual percentage deviation change was +/- 4.4% per 28 days.

Limited role of fetal blood sampling in prediction of outcome in intrauterine growth retardation

Fetal acid-base status was evaluated on 66 blood samples taken for rapid karyotyping from 58 growth-retarded fetuses. Before blood sampling, doppler blood flow studies of the umbilical artery showed end-diastolic frequencies to be absent in 32 fetuses (group 1) and present in 26 (group 2). Fetuses with chromosomal (n = 4) or structural (n = 8) abnormalities were excluded from subsequent analysis. Gestational age at blood sampling (27.8 [95% CI 26.5-29.1] vs 32.2 [30.4-34.1] weeks) and time from sampling to delivery (median 2 (range 0-35] vs 14 [0-77] days) were significantly lower in group 1 than group 2. There were no perinatal deaths in group 2 whereas mortality in group 1 was 65.4%. There were significant differences between the groups at blood sampling in pH, pO2, pCO2, base equivalents, and nucleated-red-cell count, but within group 1 these measurements were similar in surviving fetuses and those who died perinatally. Since acid-base determination does not predict perinatal outcome in growth-retarded fetuses, fetal blood sampling has a limited role in monitoring fetal wellbeing.

Acute fetal hemodynamic alterations after intrauterine transfusion for treatment of severe red blood cell alloimmunization

One of the compensatory hemodynamic mechanisms seen in the anemic human fetus is an increased cardiac output. With Doppler techniques, cardiac output was measured in 21 fetuses before and immediately after 38 intrauterine transfusions for severe red cell alloimmunization. Umbilical venous pressures were measured before and after transfusion; amniotic fluid pressure was also quantitated. After subtraction of amniotic pressure, umbilical venous pressure increased by 1.7 +/- 2.8 mm Hg (p less than 0.01). Left and right ventricular output declined by 19% and 22%, respectively (p less than 0.001). Four factors are known to affect cardiac output: heart rate, cardiac contractility, preload, and afterload. Fetal heart rate and mean acceleration, a measure of myocardial contractility, were unchanged after transfusion. A calculated mean increase in the fetoplacental volume of 18% in conjunction with an increase in umbilical venous pressure would indicate that cardiac preload was increased. We propose that intravascular intrauterine transfusion leads to an increased cardiac afterload, possibly by increasing blood viscosity. The fetal heart responds to the increased afterload by a decrease in stroke volume, leading to a fall in cardiac output.

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.

Vaginal breech delivery: a five-year prospective evaluation of a protocol using computed tomographic pelvimetry

In 1983 a protocol was established at our institution that used computed tomographic pelvimetry to evaluate patients presenting with a singleton term frank breech fetus for an attempt at vaginal delivery. The criteria for a trial of labor were singleton fetus, term gestation (37 to 42 weeks' gestation from the first day of the last menstrual period), frank breech presentation, estimated fetal weight 2000 to 4000 gm, non-extended fetal head, and adequate computed tomographic pelvimetry. Two digital radiographs and a tomographic cross-section were taken of each patient, i.e., an anteroposterior view, a lateral view, and an axial section through the femoral head at the level of the fovea capitalis. Adequate pelvimetry was defined as: anteroposterior diameter of the inlet greater than or equal to 10.0 cm, transverse diameter of the inlet greater than or equal to 11.5 cm, transverse (interspinous) diameter of the midpelvis greater than or equal to 9.5 cm, and posterior sagittal diameter of the midpelvis greater than or equal to 4.0 cm. The purpose of this prospective analysis was to determine the obstetric and perinatal outcome of those breech fetuses that were evaluated with these criteria during the study period of January 1984 through July 1989. During this period the incidence of breech deliveries at our institution was 2.71% (394/14,542). Of these 394 breech deliveries, 122 patients underwent computed tomographic pelvimetry. Eighty-five patients had adequate pelvimetry, fulfilling the protocol criteria, and formed the study group. Eighty-one percent (69/85) of the study group had successful vaginal deliveries (group 1). Nineteen percent (16/85) required cesarean delivery after a trial of labor (group 2) (10 with fetal distress and six with arrested labor disorders). Of the 37 patients who had inadequate computed tomographic pelvimetry and underwent cesarean delivery without a trial of labor (group 3), 54% (20/37) had an extended fetal head, 21.6% (8/37) had an inadequate transverse diameter of the inlet, 13.5% (5/37) had an inadequate midpelvic posterior sagittal measurement, and 10.8% (4/37) had an inadequate interspinous diameter. Perinatal outcome including Apgar scores, cord gases, length of hospital stay, neonatal complications, was evaluated. No difference in infant complications was noted between the group delivered vaginally and the groups delivered abdominally. The only maternal complications in our study group were chorioamnionitis, endomyometritis, and postpartum anemia. There were no significant differences in the incidence of chorioamnionitis among the three groups of patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Estimated fetal weight in twin pregnancy: how good are we?

Ultrasonic assessment of fetal weight derived from multiple measurements of the fetus has become accepted in clinical practice as being useful in singleton pregnancies. Several different formulae for estimating fetal weight have been derived from differing measurements of the fetus, such as biparietal diameter, trunk circumference, and femur length. To date, there has been no attempt to evaluate such a technique in multiple pregnancy. This study aims to see whether the formulae derived for singleton pregnancy are applicable to twin pregnancies. Estimated fetal weight will be derived by mathematical modelling from ultrasonic measurements made within a week of delivery and the results compared with the actual birthweight to give an indication of how good such estimated fetal weights are. Factors to be considered in the analysis include whether there are differences between Twin I and Twin II, differences of presentation with twins and differences by gestation at delivery.

Intrauterine fetal growth in concordant twin gestations

We longitudinally assessed intrauterine ultrasonic growth parameters (biparietal diameter, head circumference, abdominal circumference, and femur length) in 60 pairs of concordant twins. Head circumference to abdominal circumference and femur length to abdominal circumference ratios were calculated. Estimated fetal weight curves were created with the formula of Shepard et al., incorporating biparietal diameter and abdominal circumference, as well as that of Hadlock et al., incorporating femur length and abdominal circumference. Biparietal diameter was obtained in only 79% of fetuses, whereas femur length and abdominal circumference were obtained in 96% and 99% of fetuses, respectively. The intrauterine growth of abdominal circumference appears to be linear between 18 and 40 weeks, fitting the simple equation abdominal circumference = -4.5 + 0.97 gestational age (gestational age in weeks). The mean femur length to abdominal circumference ratio is 22.4 +/- 1.5 and appears to be gestational age independent between 20 and 40 weeks. The head circumference to abdominal circumference ratio decreases as gestational age advances in a linear fashion. Estimated fetal weight curves by the formulas of both Shepard et al. and Hadlock et al. fit second-order polynomial equations. Neither formula appears to be superior in estimating fetal weight in twin gestations, although that of Hadlock et al. can be used more frequently since biparietal diameter cannot always be obtained in both twins.

Screening tests for intrauterine growth retardation: a comparison of umbilical artery Doppler to real-time ultrasound

In a study designed to compare Doppler umbilical artery velocimetry to ultrasound morphometric measurements in the prediction of intrauterine growth retardation, 636 paired ultrasound and Doppler umbilical artery examinations were performed between 24 and 40 weeks gestational age. Intrauterine growth retardation was defined as birth weight less than the tenth percentile per gestational age and 25 (9.2%) of the infants born in our study met this criteria. In general, when the gestational age was limited to less than 30 weeks, none of the tests were highly predictive of intrauterine growth retardation. Doppler umbilical artery systolic-to-diastolic ratios of greater than 3 had the highest sensitivity. However, due to inclusion of a large number of false-positives, it was considered a poor test. After 30 weeks, fetal abdominal circumference less than the tenth percentile had a greater sensitivity (45%) and positive predictive value (28%) than Doppler systolic-to-diastolic ratios greater than 3 (36% and 18%, respectively). Doppler ultrasound umbilical artery systolic-to-diastolic ratios are not more predictive of intrauterine growth retardation than ultrasound morphometric measurements.

Ultrasonographic estimation of fetal weight in the clinically macrosomic fetus

The purpose of this study is to evaluate models for the prediction of birth weight in fetuses suspected of being macrosomic. A total of 141 patients with standard measurements of the head, abdomen, and femur were studied. Linear regressions were performed with single parameters, squares, and all possible cross products in the generation of models with log (birth weight) and birth weight as dependent variables. These models were then compared with a group of previously published equations. Clinically, all models performed poorly. However, two models were significantly less accurate in the prediction of birth weight (p less than or equal to 0.05). The best results were obtained by equations that used abdominal circumference and femur length measurements. There was no improvement in models that contained log (birth weight) or birth weight as dependent variables or models with complex variables such as squares or cross products of measured parameters. In conclusion, when evaluating patients at risk of macrosomia, the best estimates of fetal weight can be obtained by models that contain abdominal circumference and femur length.

Prediction of hematocrit decline after intravascular fetal transfusion

Fetal blood sampling and intravascular transfusion via cordocentesis allow more precise fetal evaluation and treatment in isoimmunized pregnancies. However, the timing of repeat transfusion has remained empiric. In this report we review our experience with fetal transfusions in isoimmunized pregnancies to evaluate the ability to predict fetal hematocrit decline and thereby determine the optimum timing for repeat transfusions. Between March 1986 and March 1988, 60 intravascular fetal transfusions were performed in 20 patients. Fetal transfusions were excluded from analysis if blood samples were unable to be obtained before and after transfusion, as well as at the beginning of the next transfusion or birth. Fifty-three procedures were analyzed. Two equations were used to predict the fetal hematocrit at the subsequent transfusion. The difference between observed and predicted hematocrits at the beginning of a subsequent transfusion or birth was -0.9% +/- 5.8% with equation 2, which was the more accurate formula in the majority of fetuses. Prediction of fetal hematocrit decline may be used to determine the optimum timing of repeat transfusion.

Estimating gestational age in the term pregnancy with a model based on multiple indices of fetal maturity

A prospective ultrasonographic study was conducted in 100 normal pregnant women with gestational ages that ranged from 36 to 42 weeks in which multiple biometric measurements were obtained. Dimensions of the distal femoral, proximal tibial, and proximal humeral epiphyseal ossification centers, as well as the placental and colonic grades, were also evaluated. A high statistical correlation was found between gestational age and each of the five variables (p less than 0.001). With a stepwise linear logistic regression analysis, we determined that gestational ages (36 to 39 weeks and 40 to 42 weeks) could be ascertained with a high probability with the use of a combination of the proximal humeral epiphysis and colonic grades. Probability estimates were not significantly affected by the addition of the distal femoral, proximal tibial epiphyses, placental grade, or amniotic fluid volume. From these data, probability prediction tables were generated. The results of this study provide an alternate method by which gestational age may be estimated in late pregnancy.

Ultrasonographic measurement of fetal femur length in growth disturbances

Ultrasonographic measurement of fetal femur length is a recognized technique for determination of gestational age and fetal growth. A total of 280 pregnant women were studied, each of whom had pathologies with the potential to either accelerate or delay fetal growth. There were 1000 measurements of the fetal femur length performed on these 280 fetuses. A total of 125 fetuses were found to have a growth disturbance-91 with asymmetrical intrauterine growth retardation and 34 with macrosomia. Comparison of fetuses with either intrauterine growth retardation or macrosomia with appropriate-for-gestational-age fetuses showed that the femur length is not statistically affected by intrauterine growth abnormalities.

A comparison of three methods of assessing inter-observer variation applied to ultrasonic fetal measurement in the third trimester

The inter-observer variation of fetal biparietal diameter, head circumference, abdominal circumference, and femoral length measured in the third trimester by ultrasound was studied by three different methods--coefficient of variation, correlation coefficient, and the 95% limits of agreement. The coefficients of variation were 1.6 to 3.7%, the correlation coefficients were 0.89 to 0.98 with P values of less than 0.001, yet the limits of agreement when applied to centile charts were found to be too wide to separate reliably small fetuses from those that were not small. We conclude that the limits of agreement is the preferred method of assessing inter-observer variation, and we suggest that future research into growth retardation move away from ultrasonic measurements of the fetus.

Fetal weight estimation in twin pregnancies

In this study the fetal weight was estimated by ultrasound measurements of the biparietal (BPD) and abdominal diameters (AD) in 154 consecutive twin pregnancies. In 80 twins an attempt to estimate fetal weight was made 0-4 days before delivery (26% of all twins examined). In 84% (67 infants) it was possible to estimate the fetal weight using the formula (0.0108 X AD1.72 X BPD0.99). 60% of the birth weights deviated less than 10% from the estimated fetal weight and 83% deviated less than 15%. The prediction error was nearly constant, expressed as percent of actual weight in the different weight groups (8.5-9.8%). In 19 LGA infants, 69% of the birth weights deviated less than 10% from the estimated fetal weight and 70% deviated less than 15%.

Birth weight prediction from remote ultrasonographic examination

Multiple linear regression by the least squares method was used to remodel five existing static equations to permit birth weight estimates from remote ultrasonographic parameters. By incorporating lapse time (examination-to-delivery interval), the new equations can be used to estimate birth weight 0 to 35 days after ultrasonographic examination. For each model, R2 approached 1.0. The generated equations were tested on 167 nonmodel cases. Among the three best equations, 65% to 67% of estimates were within 100 mg/kg birth weight. The mean absolute error ranged from 86 to 91 gm/kg. With a mean lapse time of 16.8 +/- 11 days, the accuracy of birth weight estimates equaled or exceeded that reported for existing static formulas. The accuracy of the estimates was maintained across the entire range of lapse times and birth weights observed. In intrapartum situations when ultrasonography is unavailable or technically difficult, birth weight can be estimated from remote ultrasound parameters.

Fetal cardiac output in the isoimmunized pregnancy: a pulsed Doppler-echocardiographic study of patients undergoing intravascular intrauterine transfusion

The mechanism of development of hydrops fetalis in severe isoimmunization has been subject to speculation. We performed pulsed Doppler assessment of cardiac output in 13 severely isoimmunized fetuses before and after intravascular transfusion and compared the results with 37 control fetuses between 20 and 34 weeks' gestation. The cardiac index of the anemic fetuses was significantly greater than that of the control group. A significant (right ventricle, p less than 0.01; left ventricle, p less than 0.02) increase in indexed output was noted from both ventricles and in the combined ventricular output (mean +/- SEM 644 +/- 35.3 ml/kg/min in control fetuses versus 879 +/- 86.0 ml/kg/min in anemic fetuses, p less than 0.006). An increase in cardiac output was also noted when anemic fetuses were compared with gestational age-specific norms. We conclude that severely anemic fetuses of isoimmunized pregnancies tend to have significantly higher cardiac output than do unaffected fetuses and that this high output state may play a part in the development of hydrops fetalis.

Pulsed Doppler flow-velocity waveforms in the prediction of fetal hematocrit of the severely isoimmunized pregnancy

We previously reported a significant relationship between the hematocrit levels of anemic fetuses and information derived from ultrasonographic and Doppler flow-velocity waveforms. In this study we prospectively tested two formulas for the prediction of hematocrit values, by use of gestational age, presence or absence of hydrops, and Doppler indices. Although one of the two formulas predicted hematocrit values significantly, the only component of the formula that made a significant contribution was fetal hydrops. We conclude that currently available fetal Doppler measurements are unable to be applied in the prospective prediction of hematocrit values in anemic fetuses of isoimmunized pregnancies.

Estimating fetal weight in patients with preterm premature rupture of the membranes

Fetal weight estimation was performed in 58 women with preterm premature rupture of the membranes within 4 days of delivery. Of twelve formulas evaluated, only two met the requirements for clinical use (i.e., they had a small mean percent error and a high correlation). However, both had high random error, which may be attributable to the very low birth weights studied.

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

This report sought to determine whether estimates of fetal weight are enhanced by using ultrasonographic formulas targeted to the large-, appropriate-, and small-for-gestational-age fetus in both preterm and term pregnancies. Ultrasonographic fetal measurements from 575 singleton pregnancies were obtained within 7 days of delivery. The first 194 fetuses were classified into three groups on the basis of the growth percentile rank of the abdominal circumference (greater than or equal to 90%, greater than 5% and less than 90%, and less than or equal to 5%). Regression analyses were performed to generate three formulas for estimating fetal weight on the basis of the following: Gestational age (weeks) + Head circumference (cm) + 2 x Abdominal circumference (cm) + Femur length (cm). This mathematic model allowed formulation of accurate and concise tables relating the sum of these measurements to estimated birth weight. The accuracy of these formulas was then prospectively compared, first, with the formula published by Hadlock et al. (in 32 large-, 279 appropriate-, and 70 small-for-gestational-age fetuses) and second, with the formula of Weiner et al. (in 82 preterm fetuses). The difference between actual and estimated birth weights generated by the three study formulas had no systemic error (t test, p greater than 0.05). Cumulatively, there was a statistically significant reduction of random error in the birth weight estimates by use of the three study formulas versus the best single formulas of Hadlock et al. (2 SD reduced from 21.6% to 19.8% and absolute 2 SD reduced from 15.6% to 12.2%). Additionally, the three study formulas resulted in a statistically significant reduction in the absolute 2 SD error compared with the best formula by Weiner et al. in fetuses less than or equal to 34 weeks' gestation (2 SD reduced from 19.1% to 13.6%).

Prediction of fetoplacental blood volume in isoimmunized pregnancy

Direct intravascular fetal transfusion under ultrasound guidance allows precise evaluation of both fetal anemia and adequacy of therapy. In addition, the change in hematocrit after transfusion may be used to estimate the circulatory fetoplacental blood volume. In this study we present the estimates of fetoplacental blood volume calculated at the time of intravascular fetal transfusions. Between March 1986 and March 1988, 60 intravascular fetal transfusions were performed in 20 patients. The 56 procedures in which fetal hematocrits were obtained both before and after transfusion were analyzed. The mean fetoplacental blood volume before transfusion was 94.0 ml/kg. Furthermore, the fetoplacental blood volume per kilogram fetal weight decreased with advancing gestation. These estimates of fetoplacental blood volume and changes relative to gestational age may be useful in the treatment of the severely isoimmunized fetus. Reliance on the more recently generated fetoplacental blood volumes may allow more accurate predictions of transfusion volumes and estimation of the hematocrit after transfusion.

Efficacy of the fetal-pelvic index as a predictor of fetal-pelvic disproportion in women with abnormal labor patterns that require labor augmentations

The fetal-pelvic index, which compares fetal head and abdomen circumferences with respective maternal inlet and midpelvic circumferences, was introduced in 1986 as a means of identifying the presence or absence of fetal-pelvic disproportion. In this study the efficacy of the fetal-pelvic index was evaluated in 46 patients with abnormal labor patterns that required labor augmentations and was compared with that of two other means (Colcher-Sussman x-ray pelvimetry and ultrasonographically derived estimated fetal weight greater than or equal to 4000 gm). Of the 24 women who required operative intervention (19 cesarean sections and five operative vaginal procedures), 17 had positive fetal-pelvic index values (sensitivity = 0.71). Six of the seven fetuses of patients with false-negative fetal-pelvic index values persisted in an occipitoposterior presentation, and these patients failed to progress in labor. Of the 22 patients in whom vaginal deliveries were spontaneous, 21 had negative fetal-pelvic index values (specificity = 0.95). Of the 18 women with positive fetal-pelvic index values, 17 required operative intervention (positive predictability = 0.94). In contrast, when used alone, neither x-ray pelvimetry nor ultrasonographically derived estimated fetal weight greater than or equal to 4000 gm provided accurate identification of fetal-pelvic disproportion.

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.

Efficacy of the fetal-pelvic index in patients requiring labor induction

The fetal-pelvic index is a recently described means of identifying the presence or absence of fetal-pelvic disproportion. In this follow-up study, the efficacy of the fetal-pelvic index was evaluated in 49 patients requiring labor induction and was compared with two other methods used to identify fetal-pelvic disproportion (Colcher-Sussman x-ray pelvimetry and ultrasound-derived estimated fetal weight). Twelve of 14 patients who required operative intervention also demonstrated a positive fetal-pelvic index (sensitivity = 86%). Spontaneous vaginal deliveries occurred in 35 patients, all of whom demonstrated negative fetal-pelvic index values (specificity = 100%). Overall the predictability of the fetal-pelvic index was 96%. In comparison, when used alone, neither x-ray pelvimetry nor ultrasound-derived estimated fetal weight accurately detected the presence or absence of fetal-pelvic disproportion in patients requiring labor induction.

Prenatal diagnosis and management of bilateral hydronephrosis

This report reviews the management of the fetus with congenital hydronephrosis (CH), a challenging diagnostic and therapeutic problem. Experimental models of obstructive uropathy have produced histologic changes similar to those seen in kidneys of human neonates with congenital hydronephrosis. Relief of obstruction in utero in these models has been shown to prevent some of the dysplastic changes caused by obstruction. These studies have formed the theoretical basis for in utero decompression to restore amniotic fluid dynamics to prevent death from pulmonary hypoplasia, and reverse or arrest dysplastic morphogenesis. The development of prognostic criteria has greatly aided in selection of appropriate fetuses for intervention. These criteria include: (1) Na less than 100 mEq/l; (2) Cl less than 90 mEq/l; (3) osmolarity less than 210 mosmol; (4) sonographic appearance of the fetal kidneys; (5) amniotic fluid status; (6) urine output at fetal bladder catheterization. All fetuses should have ultrasonography to exclude other anomalies, and karyotype analysis to exclude chromosomal abnormality. If amniotic fluid volume is normal, the pregnancy is followed with serial ultrasound examinations. If oligohydramnios develops, a prognostic evaluation is performed, including fetal bladder catheterization. If the fetus has poor residual renal function, on the basis of prognostic criteria, appropriate counseling may be given. If the fetus has good residual renal function, depending on lung maturity, it can be delivered early for corrective surgery. If diagnosed prior to lung maturity in utero, decompression by either vesicoamniotic shunting or open fetal surgery may be attempted in the highly selected case.(ABSTRACT TRUNCATED AT 250 WORDS)

The predictability of the small-for-gestational-age infant by real-time ultrasound-derived measurements combined with pulsed Doppler umbilical artery velocimetry

During a 15-month period 373 level II ultrasound examinations were performed in 256 high-risk patients. In addition, pulsed Doppler spectral recordings of blood flow in the fetal umbilical arteries were made. A systolic/diastolic ratio was then calculated for each fetus. Real-time ultrasound-derived estimated fetal weight with the use of biparietal diameter and abdominal circumference was also calculated. The estimated fetal weights were categorized by placing them in a percentile for gestational age according to published nomograms. Complete birth data and outcomes were obtained in all patients. Both the systolic/diastolic ratio and ultrasound-estimated fetal weight grouped by percentile ranking for gestational age were highly predictive (p = 0.001) of babies who were subsequently born small for gestational age. Seventy-nine percent of the infants small for gestational age had umbilical artery systolic/diastolic ratios greater than or equal to 4, whereas only 21% had normal systolic/diastolic ratios. Forty-three percent of the infants who were small for gestational age had ultrasound-estimated fetal weights less than or equal to 10th percentile for the gestational age at which it was measured. Umbilical artery systolic/diastolic ratios, which reflect an increase in peripheral resistance in the placental circulation, showed a highly predictive and discriminatory index for the evaluation of the fetus suspected of having growth retardation.

Efficacy of the fetal-pelvic index for delivery of neonates weighing 4000 grams or greater: a preliminary report

The fetal-pelvic index was recently introduced as an accurate method of prospectively identifying the presence or absence of fetal-pelvic disproportion. In that report the ability to detect fetal-pelvic disproportion in patients with macrosomic fetuses was not specifically addressed. The objective of this study is to compare the efficacy of three methods used to identify the presence or absence of fetal-pelvic disproportion (the fetal-pelvic index, Colcher-Sussman x-ray pelvimetry, and estimated fetal weight greater than or equal to 4000 gm) in patients delivered of neonates weighing greater than or equal to 4000 gm after an adequate trial of labor (N = 34). Of the 18 patients requiring operative intervention, all but one had a positive fetal-pelvic index value (sensitivity = 94%). Of the 16 patients in whom vaginal deliveries were spontaneous, all but one had a negative value (specificity = 94%). On the basis of these data, the fetal-pelvic index is an accurate method of predicting the presence or absence of fetal-pelvic disproportion in patients delivered of neonates weighing greater than or equal to 4000 gm.

Sonographic estimation of fetal weight and Doppler analysis of umbilical artery velocimetry in the prediction of intrauterine growth retardation: a prospective study

A prospective study was undertaken to examine whether Doppler velocimetry studies of the umbilical artery give a better or an earlier prediction of intrauterine growth retardation (IUGR) than do sonographic estimation of fetal weight. A total of 385 examinations were performed between 30 and 42 weeks of gestation on 168 patients who were at risk for IUGR. Forty-two (25%) of the patients delivered an infant with a birth weight below the tenth percentile. Although sensitivity was lower for the systolic to diastolic ratio (55%) of the umbilical artery than for the sonographic estimation of fetal weight (76%), the umbilical artery studies had a higher specificity (92% versus 80%) and predictive value of a positive test (73% versus 58%) when the last study to delivery interval was within 2 weeks. Furthermore, among 21 IUGR pregnancies with serial studies, the umbilical systolic to diastolic ratio was abnormal at a significantly earlier gestational age than when the sonographic estimate of fetal weight identified growth retardation. These findings indicate that sonographic biometry is a more sensitive technique for identifying IUGR but that the umbilical artery waveforms are a valuable adjunct for improving the diagnostic accuracy for the prenatal detection of IUGR. These data also provide suggestive evidence that umbilical artery velocimetry may be predictive of IUGR at an earlier gestational age than sonographic estimation of fetal weight.

Ultrasonographic assessment of gestational age with the distal femoral and proximal tibial ossification centers in the third trimester

A prospective sonographic evaluation of the distal femoral and proximal tibial epiphyseal ossification centers in 228 normal pregnant women was carried out from 28 to 40 weeks' gestation. The mean gestational age at which the distal femoral epiphysis and proximal tibial epiphysis were imaged was 34 and 38 weeks, respectively. The distal femoral epiphysis was not identifiable before 28 weeks but was observed in 72% of fetuses at 33 weeks and in 94% of fetuses at 34 weeks' gestation. The presence of a distal femoral epiphysis measuring 1 or 2 mm was associated with a gestational age of greater than 33 weeks in 87.0% of fetuses, whereas a distal femoral epiphysis measuring greater than or equal to 3 mm was associated with a gestational age greater than 37 weeks in 85% of fetuses. The proximal tibial epiphysis, which was absent before 34 weeks' gestation, was observed in 56% of fetuses at 36 weeks, in 80% of fetuses at 37 weeks, and in 100% of fetuses at 39 weeks of gestation. The presence of a proximal tibial epiphysis of 1 or 2 mm was associated with a gestational age of greater than 36 weeks in 88% of fetuses, whereas a proximal tibial epiphysis greater than or equal to 3 mm was associated with a gestational age of greater than 38 weeks in 94% of fetuses. The sonographic evaluation of distal femoral epiphysis/proximal tibial epiphysis can be used as independent markers for estimation of gestational age during the third trimester, a period in which standard fetal biometric estimates of gestational age are least accurate.

Ultrasonic prediction of birth weight in preterm fetuses: which formula is best?

Data from previous studies have suggested that birth weight prediction was enhanced by using formulas specifically derived from preterm fetuses. However, no prospective comparison of different formulas was performed. We obtained ultrasonic data on 61 pregnancies at risk for preterm delivery with a gestational age of 29.0 +/- 3.0 weeks (mean +/- SD). In all women birth weight was predicted within 7 days of delivery. Of the 61 pregnancies, 49 (80%), 41 (67%), 30 (49%), and 17 (28%) weighed less than 1750, 1500, 1250, and 1000 gm, respectively; 14 published formulas were compared for accuracy in predicting birth weight in these four categories. The formulas with the smallest absolute mean percent errors incorporated head and abdominal circumferences and femur length. The formula of Weiner et al., derived from low birth weight infants, produced the smallest absolute mean percent error and SD, 10.9% +/- 7.9%; this error was further reduced to 7.7% +/- 6.5% in infants weighing less than 750 gm. These findings suggest that birth weight in the preterm fetus is best predicted by a formula targeted to such a population.

Formulas for fetal weight estimation by ultrasound measurements based on neonatal specific gravities and volumes

To improve the accuracy of fetal weight estimation by ultrasound measurement, especially in low birth weight infants, including those with intrauterine growth retardation, two new formulas were developed from a new point of view. The formulas were established by (1) actual measurements of the volumes of the neonatal head and trunk with limbs, (2) analysis of the relationship between the sizes of the parts of the fetal body measured by ultrasound examination before birth and the volumes of the parts of the neonatal body, and (3) calculation of the specific gravities of the parts of the neonatal body. The prospective study showed a high correlation between estimated weights and actual birth weights with a small range of error in infants weighing between 450 and 4800 gm.

The use of fetal neuromuscular blockade during intrauterine procedures

Advances in fetal therapy have led to the utilization of such techniques as intravascular transfusion of the Rh-affected fetus, bladder shunt placement in the fetus with obstructive uropathy, and percutaneous umbilical blood sampling. Fetal movement makes these procedures technically more difficult while increasing the risk of fetal injury. However, maternal sedation rarely results in adequate suppression of fetal activity. Thus we tested the sedative effects of intramuscular d-tubocurarine (3 or 1.5 mg/kg) or pancuronium bromide (0.3 mg/kg) injected into the fetal gluteal region under ultrasound guidance in conjunction with 70 invasive in utero procedures. Short-term paralysis of the fetus was induced in all cases. No deleterious effects of this technique were noted on initial examination of the neonates. Neuromuscular blockade was found to be a very useful adjunct to both diagnostic and therapeutic procedures involving the fetus.

Fetal weight estimation formulas with head, abdominal, femur, and thigh circumference measurements

Most current sonographic techniques for estimating fetal weight involve measurements of the head, abdomen, and femur length both alone and in combination. The value of the fetal thigh circumference measurement in addition to the head, abdominal, and femur length measurements has not been investigated previously. Eighty-nine patients were scanned within 72 hours of delivery, and the following ultrasonic fetal parameters were obtained in all fetuses: biparietal diameter, head circumference, abdominal circumference, femur length, and thigh circumference. With multiple stepwise regression analysis, the best-fit formulas were developed with one, two, three, four, and five parameters, respectively. The best results were obtained by combining measurements of all five parameters: biparietal diameter, head circumference, abdominal circumference, femur length, and thigh circumference. The mean error of this formula was 6%, the mean deviation 0.3%, and the SD 7.8%. These data suggest that the addition of thigh circumference to measurements of the head, abdomen, and femur length improves the accuracy of fetal weight estimates.

In utero ponderal index as a prognostic factor in the evaluation of intrauterine growth retardation

The in utero ponderal index has become a method of estimating fetal growth. Several methods have been used in the formulation of the in utero ponderal index. In the present study, 1040 pregnant women underwent ultrasonic examination between 24 and 41 weeks of gestation, and the in utero ponderal index was determined by dividing the estimated fetal weight by the third power of the femur length, rendering a relatively constant value of 8.345 +/- 2.5 (2 SD). Fifty-one cases were defined as intrauterine growth retardation due to an estimated fetal weight lower than the tenth percentile for gestational age. The in utero ponderal index proved to be a valuable index in the prediction of fetal outcome in those cases of intrauterine growth retardation in which the in utero ponderal index was smaller than 1 SD from the average of 8.345. Fetal and neonatal well-being was clearly compromised when intrauterine growth retardation was associated with a low in utero ponderal index.

Ultrasound evaluation of pregnancies at risk for homozygous alpha-thalassaemia-1

Twenty-six pregnant Chinese women who were at risk of giving birth to a fetus affected with homozygous alpha-thalassaemia-1 were examined serially by ultrasound. Six of these 26 pregnancies were affected. In one third of the affected pregnancies progressive fetal ascites appeared before 24 weeks gestation and these pregnancies were terminated. In the remaining two thirds abnormal estimated fetal weight-placental volume (EFW-PV) ratio and fetal growth retardation as evidenced by a falling biparietal diameter (BPD), femur length (FL) but a normal abdominal circumference (AC) was apparent by 28 weeks gestation. Increased transverse cardiac (TC) diameter was another consistent finding but appeared late. All these features appeared before the onset of fetal ascites. A normal EFW-PV ratio and fetal growth until 28 weeks gestation was a reassuring sign of normality. Abnormal EFW-PV ratio was the earliest sign to appear in affected pregnancies and a normal ratio until 28 weeks gestation had a 100 per cent predictive value.

Prenatal sonographic assessment of the fetal thorax: normal values

Fetal thoracic circumference and thoracic length measurements were obtained by ultrasonographic examination on 576 women between 16 and 40 weeks gestation. Nomograms for thoracic circumference and thoracic length with respect to gestational age were developed. Growth of both thoracic parameters was observed to be linear throughout gestation. In normal pregnancy the ratios of thoracic circumference to abdominal circumference and thoracic length to humerus length remained virtually constant at 0.89 and 0.93, respectively.

Diagnostic ultrasonography

The use of diagnostic ultrasound has contributed to the evaluation of the fetal condition in two ways--the detection of fetal abnormality and the assessment of fetal growth and development. Routine early pregnancy scanning enables most major structural anomalies to be detected and provides accurate gestational dating. Maternal serum alphafetoprotein screening complements ultrasound in identifying abnormalities, and may also be an indicator of a growth problem in later pregnancy. In high-risk pregnancies, or when growth retardation or acceleration is suspected, abnormalities should always be considered and investigations should include karyotyping. Fetal growth may be assessed by multiple parameters, including measurement of fetal head, trunk, limbs, and amniotic fluid volume, in addition to grading of the placenta. Fetal responses to stimulation can be visualized and quantified. No single parameter may be used alone to predict fetal outcome, but by using this multiple-parameter approach, contributing to a biophysical profile of the fetus, the outcome of pregnancy may be predicted with greater accuracy.

A randomized study of fetal abdominal diameter and fetal weight estimation for detection of light-for-gestation infants in low-risk pregnancies

A total of 2771 pregnant women with gestational age estimated by ultrasound measurement of the fetal biparietal diameter (BPD) before the 22nd week of gestation were re-examined by ultrasound in the 32nd and 37th week of pregnancy at which time the fetal BPD and abdominal diameter (AD) were measured. An additional examination was performed at 34 weeks if the fetal weight in the 32nd week was estimated to be less than 95% of the expected mean weight. Light-for-gestational age (LGA) was suspected if the estimated birth-weight was less than 85% of the expected mean birthweight. This applied to 186 uncomplicated pregnancies in which there was no clinical suspicion of poor intrauterine growth. These pregnancies were randomly allocated to a treatment group (AD and estimated weight reported) or to a control group (AD and estimated weight withheld). Induction of labour was significantly more common in the treatment group (41%) than in the control group (15%). No statistically significant difference was found in the use of instrumental vaginal delivery or caesarean section. There was a suggestion of marginal benefit in terms of neonatal morbidity but this was not statistically significant.

Sonographic determination of fetal weights in diabetic pregnancies

Accurate antenatal diagnosis of the macrosomic infant of a diabetic mother should lead to a decrease in perinatal morbidity. Several formulas for weight estimation based on sonographic measurements are in common use, but none of them has been devised specifically for the infant of a diabetic mother. We assessed the accuracy of conventional formulas at estimating fetal weight in 160 of these infants and found their relative errors (error as a percentage of birth weight) had standard deviations of 12.2% to 13.1% (greater than has been reported in the general population) with no statistically significant difference among formulas. We also devised customized formulas generated from a "training set" of 80 patients and tested on a second set of 80 patients. The best formula yielded a standard deviation of 11.0%. The difference between customized and conventional formulas was not statistically significant. With use of one conventional formula, the likelihood of macrosomia was found to be 77% when the estimated weight was greater than 4000 gm and 86% when the estimated weight was greater than 4500 gm. We conclude that fetal weight prediction is even less accurate in the infant of a diabetic mother than in the general population and that "customized" formulas fare no better than conventional formulas in diabetics. Despite this, estimated weights can offer guidance in predicting fetal macrosomia and therefore aid in obstetric management.