An evaluation of two equations for predicting fetal weight by ultrasound

Choosing route of delivery for the macrosomic infant of a diabetic mother: Cesarean section versus vaginal delivery

The macrosomic fetus of a diabetic woman faces increased risk for injury at the time of vaginal birth. Cesarean section offers the promise of avoiding trauma to the fetus, but can result in increased morbidity in the mother as compared to vaginal delivery. In this article, the advantages and disadvantages of the two routes of delivery for the overgrown fetus of a diabetic mother are discussed. Specifically, data regarding risk of permanent neurological damage to the infant from vaginal delivery, and maternal morbidity from elective, pre-labor Cesarean delivery are critically examined. In addition, methods for diagnosing macrosomia by ultrasound are discussed, along with the benefits and pitfalls of ultrasonic fetal weight estimation in the setting of diabetes. Finally, management approaches for selecting route of delivery for the macrosomic fetus are described and analyzed.

Comparison of fetal growth estimates based on birth weight and ultrasound references

OBJECTIVE

To compare three different methods for modeling fetal weight gain during the third trimester of pregnancy.

METHODS

Ultrasound and live birth weight data were used to construct three models for defining fetal growth during the third trimester: longitudinal ultrasound estimates of fetal weight obtained serially at 3-4 week intervals in 50 uncomplicated, well-dated pregnancies between 19 and 40 weeks' gestation; cross-sectional ultrasound estimates of fetal weight obtained from 2018 ultrasound examinations of singleton, non-anomalous fetuses between 24 and 39 weeks' gestation; and cross-sectional birth weight data obtained from 9553 live singleton, non-anomalous neonates between 24 and 43 completed weeks. Analysis was performed by pairwise partial f test to compare regression curves and zeta test for comparison of mean weekly weight gain. A value of p < 0.05 was accepted for significance.

RESULTS

Derived regression lines depicting fetal size across gestation were significantly different from each other (f tests, p < 0.05). Estimates of mean fetal weight were significantly different between the three different models at specific gestational ages. Significant weekly variations in fetal weight gain were observed within the raw cross-sectional data sets, both for ultrasound-estimated fetal weight (range 91-278 g/week) and birth weight (65-309 g/week).

CONCLUSIONS

Each of the methods used to model normal fetal weight gain in the third trimester defined a distinct pattern of fetal growth. Normal fetal growth, defined longitudinally, was most closely matched by a combination of cross-sectional ultrasound-derived estimated fetal weight in preterm gestation below 34 weeks' gestation and live birth weight at or beyond 34 weeks.

Ultrasonographic nomograms of the fetal fourth ventricle: additional tool for detecting abnormalities of the posterior fossa

OBJECTIVE

To characterize normal growth of the fetal fourth ventricle on ultrasonography throughout pregnancy.

METHODS

Consecutive biometric measurements and fetal organ scans were obtained from 299 patients undergoing fetal anatomic surveys between 13 and 40 weeks' gestation. Using 7- and 3.5-MHz transducers for early (13- to 17-week) and late (>17-week) examinations, respectively, we scanned the fetal head in the axial plane with special focus on the posterior fossa of the brain. The fourth ventricle was identified, and its anteroposterior diameter and width were measured. A "triangle" formula was used for calculating its circumference and area.

RESULTS

The fourth ventricle was shown as a hypoechoic triangle below the level of the cerebellum. A linear regression line of the fourth ventricle was observed across gestational age, and a first-degree correlation was found between gestational age and anteroposterior diameter of the fourth ventricle (r = 0.894; P < .0001; y = -0.84 + 0.23 x gestational age), its width (r = 0.657; P < .0001; y = 3.82 + 0.14 x gestational age), its circumference (r = 0.843; P < .0001; y = 5.11 + 0.58 x gestational age), and its area (r = 0.844; P < .0001; y = -10.11 + 1.17 x gestational age). Twelve enlarged fourth ventricles were found between 14 and 16 weeks, but results of follow-up scans at 20 weeks were normal.

CONCLUSIONS

An isolated enlarged fourth ventricle in the early second trimester might represent a normal variant; it should be followed, but decisions about the fate of the pregnancy should not be based solely on this finding.

Neonatal anthropometric measurements to predict birth weight by ultrasound

OBJECTIVE

To develop a more accurate ultrasound birth weight (BW) model using neonatal anthropometric measurements.

STUDY DESIGN

Two hundred thirty-one newborns were evaluated. Measurements included weight; head, chest, and abdominal circumferences (umbilicus and liver), humerus, and femur lengths. Infants were randomly assigned into two groups (G(1) and G(2)). Anthropometric measurements that are obtainable by ultrasound were generated from G(1). Stepwise regression and a bootstrap analysis were used to create the prediction models. The models were validated using G(2).

RESULTS

The final stepwise regression model included FL and circumferences of the head, chest, and abdomen. The correlations were: G(1): R(2)=0.91, p<0.001; G(2): R(2)=0.90 p<0.001. There was no difference between derived and actual BW in G(1) (p=0.42) or G(2) (p=0.28). The mean absolute percent error between the prediction model and actual BW was 3.8%.

CONCLUSION

Neonatal anthropometric models are strongly predictive of actual BW. This model will be tested prospectively using ultrasound to predict fetal weight.

Identification of fetal growth abnormalities in diabetes mellitus

Gestational diabetes complicates 3% to 5% of all pregnancies. Shoulder dystocia and fetal injuries are associated with macrosomia, a complication often encountered in diabetic pregnancies. The route of delivery is often planned in advance and based on estimated fetal weight. Fetuses of diabetic mothers are prone to macrosomia due to increased subcutaneous adipose tissue deposits, and perinatal complications are more frequent in these fetuses. For this reason, particular effort should be directed toward the diagnosis of fetal growth abnormalities in fetuses of diabetic mothers. There are numerous formulas for estimating fetal weight, and they are all error prone. An effort should be made to follow these high-risk pregnancies in a longitudinal fashion to detect any developing growth abnormality as early as possible. Whether macrosomia or intrauterine growth restriction, early detection and careful planning of mode and time of delivery is the foundation of successful lowering of perinatal morbidity and mortality.

Delivery of the macrosomic infant: cesarean section versus vaginal delivery

The macrosomic fetus of a diabetic woman faces increased risk for injury at the time of birth. Cesarean section offers the potential for avoiding trauma to the fetus, but can result in increased morbidity in the mother as compared to vaginal delivery. In this article, the advantages and disadvantages of the 2 routes of delivery for the overgrown fetus of a diabetic mother are discussed. In addition, methods for diagnosing macrosomia by ultrasound are examined, along with the benefits and pitfalls of ultrasonic fetal weight estimation in the setting of diabetes. Finally, management approaches for selecting route of delivery for the macrosomic fetus are described and analyzed.

Ultrasonographic estimation of fetal weight: acquiring accuracy in residency

OBJECTIVE

Ultrasonographic imaging is considered an objective means for fetal weight estimation. The goals of this study were to determine the accuracy of ultrasonographic estimates of fetal'weight performed by residents in training and to ascertain how rapidly the residents gained proficiency in this regard.

METHODS

A total of 300 ultrasonographic estimates of fetal weight and corresponding birth weight were collected and stratified into 4 groups by the level of residents' experience, from level 1 (inexperienced, with <6 months of exposure) to level 4 (advanced experience, with at least 24 months of training). The proportional difference between ultrasonographic estimates of fetal weight and birth weight was calculated for each case and grouped according to the level of training of the examiner. The derived data were compared by analysis of variance, linear regression, and chi2 test.

RESULTS

Significant increases in the accuracy of ultrasonographic estimates of fetal weight were observed with advancing levels of resident experience (P< .0001). Overall, 30.6% of ultrasonographic estimates of fetal weight fell within 5% of birth weight, and 60.6% fell within 10%. Among the least experienced residents (<6 months of training), 49.4% of estimates fell within 10% of birth weight; among those with 6 to 11 months of experience, 53.5% of estimates fell within 10%; among those with 12 to 23 months of experience, 64.1 % of estimates fell within 10%; and among the most experienced (>24 months), 73.6% of estimates fell within 10%.

CONCLUSIONS

There is a learning curve for ultrasonographic estimates of fetal weight, with a significant decrease in the percent error seen with advancing training among residents, reaching acceptable levels of more than 70% of estimates within 10% of birth weight after 24 months of ultrasonographic experience.

Intrauterine growth restriction (IUGR): biometric and Doppler assessment

Intrauterine growth restriction (IUGR) is a common complication in pregnancy and influences morbidity and mortality at all stages of life. Historically, the management of IUGR has been dependent on antenatal biophysical testing and umbilical artery Doppler studies. With recent Doppler studies of the fetal central circulation, including intracardiac flows and the ductus venosus, better timing of delivery to minimize morbidity may be possible. This review will provide the reader with tools to diagnose IUGR, more accurately date the IUGR pregnancy with poor dating criteria, and better assess the condition of the IUGR fetus. A brief review of animal models of IUGR is presented to demonstrate research directions for answering human clinical questions and potentially carrying therapeutic intervention from the bench to the bedside.

Menstrual age-dependent systematic error in sonographic fetal weight estimation: a mathematical model

PURPOSE

We used computer modeling techniques to evaluate the accuracy of different types of sonographic formulas for estimating fetal weight across the full range of clinically important menstrual ages.

METHODS

Input data for the computer modeling techniques were derived from published British standards for normal distributions of sonographic biometric growth parameters and their correlation coefficients; these standards had been derived from fetal populations whose ages were determined using sonography. The accuracy of each of 10 formulas for estimating fetal weight was calculated by comparing the weight estimates obtained with these formulas in simulated populations with the weight estimates expected from birth weight data, from 24 weeks' menstrual age to term. Preterm weights were estimated by interpolation from term birth weights using sonographic growth curves. With an ideal formula, the median weight estimates at term should not differ from the population birth weight median.

RESULTS

The simulated output sonographic values closely matched those of the original population. The accuracy of the fetal weight estimation differed by menstrual age and between various formulas. Most methods tended to overestimate fetal weight at term. Shepard's formula progressively overestimated weights from about 2% at 32 weeks to more than 15% at term. The accuracy of Combs's and Shinozuka's volumetric formulas varied least by menstrual age. Hadlock's formula underestimated preterm fetal weight by up to 7% and overestimated fetal weight at term by up to 5%.

CONCLUSIONS

The accuracy of sonographic fetal weight estimation based on volumetric formulas is more consistent across menstrual ages than are other methods.

Cerebellar growth in normal fetuses of multiple gestations

OBJECTIVE

The purpose of this study was to compare the cerebellar growth in twin and triplet gestations with cerebellar growth in singleton pregnancies.

METHODOLOGY

An ultrasound study was conducted in a population of normal pregnant women with singleton, twin and triplet gestations. Routine ultrasound examinations were performed in healthy pregnant women: 951 women with singleton pregnancies; 151 with twin gestations; and 28 with triplet gestations. Although multiple biometric parameters were measured throughout the course of pregnancy, in this study a single measurement (the last measurement before delivery) of the transverse cerebellar diameter (TCD) was used from each patient for statistical analysis. Growth of the TCD was determined in the multiple gestations and compared with growth in singleton pregnancies.

RESULTS

A statistically significant relationship was found between TCD and gestational age in all three groups (singleton, twin A and B, and triplets) respectively: R2 = 0.963; R2 = 0.980; R2 = 0.977. No statistical difference was found between the three sets of normative measurements.

CONCLUSIONS

There was no significant difference observed in cerebellar growth among singleton and multiple gestations. Therefore, nomograms previously established for singleton pregnancies may be useful to assess growth in multifetal pregnancies.

A model for foetal growth and diagnosis of intrauterine growth restriction

A model for foetal growth is developed and used to construct tools for diagnosis of intrauterine growth restriction. Foetal weight estimates are first transformed to normally distributed z-scores. The covariance structure over gestational ages is then estimated using a novel regression model. The diagnostic tools include individual growth curves with error bounds, probabilities to assess whether a foetus is small for its gestational age, and residual scores to determine whether current growth rates are unusual. The methods were developed sing data from 13593 ultrasound examinations involving 7888 foetal subjects. The model shows that median foetal growth velocity increases up to a gestational age of 35 weeks and then decreases during the final weeks of pregnancy. When growth is expressed as change in log weight, or equivalently as change proportional to current weight, the model reveals a constant deceleration as gestational age increases from 14 to 42 weeks.

Sonographic fetal weight estimation in a south-east Asian population

OBJECTIVES

To determine the optimal sonographic fetal weight estimation formula for a mixed south-east Asian population near term.

METHODS

Seventy-eight uncomplicated pregnancies were monitored between January 1996 and January 1997. Biparietal diameter, head circumference, abdominal circumference and femur length were measured and the following formulae were tested: Campbell, Shepherds and Hadlock. The estimated fetal weight was calculated by 12 different methods. The weight estimate was then projected forward to the time of delivery using the gestation-adjusted forward projection method. The weight estimation error was derived from the difference between the projected fetal weight and birth weight, and expressed as a percentage of birth weight.

RESULTS

The mean time interval from the time of ultrasound fetal weight estimation to delivery was 4.4 days. The birth weight ranged between 2,330 to 4,215 g. The best performing formula was Hadlock's formula using the head circumference, abdominal circumference and femur, with the perimeters calculated using the ellipse function. The standard deviation of error for this formula was 8.66%.

CONCLUSION

Even though the Hadlock formula was originally derived from an American population, it was equally useful in south-east Asian population.

Fetal aortic blood flow assessment from the relationship between fetal aortic diameter pulse and flow velocity waveforms during fetal development

BACKGROUND

Blood flow is calculated from mean velocity across the vessel and its cross-sectional area and is related to the fetal growth.

AIM

To investigate the relationship between diameter pulse waveform (DPW) and flow velocity waveform (FVW) in the fetal descending aorta during fetal development.

STUDY DESIGN

Doppler ultrasound and a phase-locked loop echo tracking system were used to measure the FVW and DPW in the fetal descending aorta, respectively.

SUBJECTS

We studied 137 normal-growth fetuses (normal group, 20-40 weeks) and 51 fetuses with high umbilical artery pulsatility index (umbilical placental insufficiency, UPI group, 26-40 weeks).

OUTCOME MEASURES

We measured the systolic (Sd), diastolic (Dd) diameters, time diameter integral (TDI) and time velocity integral (TVI) and then calculated the TVI x TDI and TVI to TDI ratio.

RESULTS

Normal fetal growth was associated with an increase in Sd, Dd, pulse amplitude, TVI, TDI and TVI x TDI. The FVW began to resemble the DPW with decreasing downstream resistance produced by growth of the placenta. The TVI was increased relative to the TDI. The differences in Sd, Dd, TDI and TVI x TDI between the normal and UPI groups were not significant. The TVI was decreased relative to the TDI. There was a decrease in the TVI as a ratio of the TDI. The Dd per unit fetal weight was high in the compromised fetuses. Fetal outcome was examined in relation to the TVI to TDI ratio. Those with a low ratio (below 10th centile) exhibited significantly more adverse indices of fetal outcome.

CONCLUSIONS

In fetal compromise there is an increase in diastolic pressure in association with high placental resistance, which causes a major increase in afterload. The efficient circulation associated with fetal growth might be represented by an increase in the ratio of the TVI to the TDI (an index of efficient circulation) when these waveform shapes resemble each other.

Accuracy and modifying factors of the sonographic estimation of fetal weight in a high-risk population

There have been a number of reviews assessing the accuracy of different methods of sonographic estimation of fetal weight, without identifying any clearly superior equation. In order to optimise accuracy in a high-risk population, we decided to compare some of the most popular early equations with the newer volume-based equations, and to try and identify factors that affect the ability of these equations to estimate fetal weight accurately We collected the scan and delivery details of 192 fetuses born within one week of a sonographic estimation of fetal weight. We then applied three of the most popular equations and two newer volume-based equations to the recorded fetal biometric parameters to assess the performance of each equation overall, and under varying maternal, fetal, and scan conditions. The equations of Shepard, Hadlock A, Hadlock B and Combs produced similar results with systematic (mean) errors in the range 1.2-1.9% and random error characterised by one standard deviation in the range of 8.6-9.5%. Dudley's volume-based equation produced a significant systematic error in the form of a mean error of 7.4%, which corresponds to a mean birthweight (BW) which is 7.4% above the mean estimated fetal weight (EFW). When we stratified the study group by birthweight, Combs' equation produced significant differences in the mean error, (p < 0.00001), that ranged from a mean overestimation in fetal weight of 8.5% for babies with BW < 1000 g to a mean underestimation in fetal weight of 6.2% for babies with BW > 3000 g. Oligohydramnios resulted in a trend towards an increased mean error for all equations which was only statistically significant for Hadlock B. The equations Shepard and Hadlock A performed best in our high-risk population. They produced the smallest systematic errors across the entire study group and were not adversely affected by variations in birthweight, liquor volume, or fetal presentation. The newer, volume-based equations were disappointing, producing large systematic errors. Large random errors in all equations continue to be the Achilles' heel that limit the value of sonographic EFW.

Assessment of fetal weight based on ultrasonic femur length after the second trimester

OBJECTIVE

The ultrasonic measurement of the fetal femur length is a sensitive and precise variable for estimation of fetal growth and development. The objective of this study is to predict fetal weight in fetuses of more than 24 weeks gestation by ultrasound measurement of the femur length.

METHOD

In this study, pregnant mothers were identified by the criteria of normalities, such as: well-known LMP, regular menstrual cycles, no use of OCP for the last 3 months, no use of alcohol or cigarettes, no drug abuse, no history of diabetes or chronic HTN. Multiple gestations, congenital anomalies and still-births were excluded. Birth-weight measurements (adjusted for maternal age, baby's sex, parity and week of gestation) were taken immediately after birth.

RESULT

The relation between fetal weight and fetal femur length has been determined by cross-sectional analysis of 900 normal fetuses (> or = 25 weeks gestation) using real time ultrasonography. Mathematical modeling of the data has demonstrated that the femur growth curve is non-linear beyond 24 weeks gestation. With the aid of a scientific calculator the data were analyzed and a simple second-grade equation has been derived: EFW (kg) = 0.042FL(2) (cm)+0.32FL-1.36, S.D. approximately +/-235 g (Honarvar's Formula 2). With the use of this data, the error in estimation of EFW given FL is +/-235 g.

CONCLUSION

This simple, new and accurate equation appears to be clinically reliable and easy to use and suggests that previous normal ultrasonic fetal femur length curves for another population may underestimate or overestimate normal fetal weight for the Iranian population. Thus, our formula is an excellent means to estimate true fetal weight.

Fetal lung volume: estimation at MR imaging-initial results

PURPOSE

To plot normal fetal lung volume (FLV) obtained with fast spin-echo magnetic resonance (MR) images against gestational age; to investigate the correlation between lung growth and fetal presentation, sex, and ultrasonographic (US) biometric measurements; and to investigate its potential application in fetuses with thoracoabdominal malformations.

MATERIALS AND METHODS

In a prospective multicenter study, 336 fetuses suspected of having central nervous system disorders underwent fast spin-echo T2-weighted lung MR imaging. Data obtained at 21-38 weeks gestation in 215 fetuses without thoracoabdominal malformations and with normal US biometric findings were selected for an FLV normative curve. FLV measurements obtained at pathologic examination with an immersion method were compared with MR FLV measurements in 11 fetuses. MR FLV values in 16 fetuses with thoracoabdominal malformations were compared with the normative curve.

RESULTS

Normal FLV increased with gestational age as a power curve; the spread of values increased with age. Interobserver correlation was excellent (R(2) = 0.96). FLV measurements at MR imaging were 0.90 times those at pathologic examination. A constant ratio (0.78) between FLV on the left and right sides was observed. No significant difference in FLV was observed between fetal presentations. Normal FLV was observed in all fetuses with cystic adenomatoid malformations and in four of six with oligohydramnios. Lowest FLV values were observed in fetuses with diaphragmatic hernia.

CONCLUSION

In fetuses with normal lungs, FLV distribution against gestational age is easily assessed in utero with fast spin-echo T2-weighted MR imaging. These preliminary findings illustrate the potential for comparing FLV measurements in fetuses at risk of lung hypoplasia with normative values.

Fetal cardiovascular function during prolonged magnesium sulfate tocolysis

The purpose of this study was to evaluate the fetal cardiovascular function during prolonged magnesium sulfate tocolysis. We performed a fetal ultrasonographic examination in 15 patients (Mg group) during magnesium sulfate tocolysis for the treatment of preterm labor. The maternal serum magnesium concentration was 5.7 +/- 0.5 mg/dl at the time of the examination. Sixteen fetuses in normal pregnancies at similar gestational ages were used as the control group. The fetal heart rate and the middle cerebral artery pulsatility index in the Mg group were lower than in the control group (p < 0.01). Fractional shortening (FS) of the right ventricle in the Mg group was lower (p < 0.01), while FS of the left ventricle was higher (p < 0.01) than in the controls. The calculated blood flow through the tricuspid orifice in the Mg group was lower than in the control group (p < 0.01). In contrast, the blood flow through the mitral orifice in the Mg group was higher than in the control group (p < 0.01). In conclusion, in spite of the fact that the right ventricular function is depressed, the fetus maintains its cardiac output during prolonged hypermagnesemia by increasing its left ventricular function. These results indicate the different fetal intracardiac and peripheral circulation, especially in the brain, from normal fetuses.

Fetal biometry: clinical, pathological, and technical considerations

Sonographic measurements of fetal ultrasound parameters are the basis for accurate determination of gestational age and detection of fetal growth abnormalities. Selection of the most useful single biometric parameter depends on the timing and purpose of measurement and is influenced by specific limitations. CRL (crown-rump length) is the best parameter for early dating of pregnancy. Biparietal diameter (BPD) maintains the closest correlation with gestational age in the second trimester. In cases of variation in the shape of the skull, head circumference is an effective alternative. Abdominal circumference is the most useful dimension to evaluate fetal growth, and femur length is the best parameter in the evaluation of skeletal dysplasia. Use of multiple predictors improves the accuracy of estimates. An individual approach to each pregnancy is recommended for fetal growth assessment. The various epidemiological factors involved in fetal growth should be considered and specific charts for different communities should be used when possible. The methods of fetal weight estimation with their limitations and potential errors are presented. Clinical application of fetal biometry in abnormal growth is discussed in cases of small- and large-for-gestational-age fetuses, chromosomal aberrations, and skeletal dysplasias.

Medical emergencies in the patient with diabetes during pregnancy

Although the outcome of pregnancies complicated by diabetes is now approaching the success seen in the normal healthy pregnant population, this improvement is only realized when careful attention is paid to the metabolic, hemodynamic, and vascular perturbations associated with the changes of pregnancy. The diabetic woman must not only pay attention to nutrition but also blunt moment-to-moment swings in blood glucose by taking frequent does of insulin. In addition, she must be under constant surveillance for a host of other complications of pregnancy, such as hypertension, retinopathy, infection, acidosis, thyroid dysfunction, nephropathy, and sudden death in utero. Any or all of these problems become medical emergencies if left untreated. Rigorous vigilance to sustain normoglycemia and normotension, examination of the retina, culture of urine, assays for ketosis, measurements of thyroid function, and monitoring of renal function and fetal status are paramount in the management of pregnancy complicated by diabetes.

Fetal weight estimation by three-dimensional ultrasound

OBJECTIVE

To assess the value of three-dimensional volume scanning in predicting fetal weight at birth.

STUDY DESIGN

Prospective cross-sectional study within 7 days of delivery. A total of 190 patients were considered for final analysis (formula-finding group: n = 125, formula evaluation group: n = 65). Inclusion criteria were a singleton pregnancy and absence of chromosomal or significant structural anomalies. Three-dimensional (3D) volumetric measurements of the fetal thigh, upper arm and abdomen were performed together with conventional two-dimensional (2D) biometry.

RESULTS

All measurements were completed successfully in each patient. Polynomial regression analysis with standard biometric parameters and volumes of the upper arm, the thigh and the abdomen was employed to yield the best-fit formula for prediction of fetal weight at birth. The new 3D formula (estimated fetal weight (EFW) = -1478.557 + 7.242 x thigh volume + 13.309 x upper arm volume + 852.998 x log10 abdominal volume + 0.526 x BPD3) proved to be superior to established 2D equations with the lowest mean error (25.8 +/- 194.4 g), the lowest mean absolute error (155.2 +/- 118.2 g) and the lowest mean absolute percentage error (6.1 +/- 5.0%) when studied prospectively in the evaluation group.

CONCLUSION

3D sonography allows superior fetal weight estimation by including soft tissue volume. Further studies at the extremes of fetal weight are needed to confirm the value of our formula in these subsets.

Diagnosis of macrosomia in the postdates population: combining sonographic estimates of fetal weight with glucose challenge testing

OBJECTIVE

To evaluate the test characteristics of sonographic estimation of fetal weight in the detection of macrosomia in nondiabetic postdates patients as a function of maternal glucose value measured after glucose challenge testing performed at 24-28 weeks of gestation.

METHODS

At or beyond 41 weeks' gestation, 656 nondiabetic patients had sonographic estimation of fetal weight. Receiver-operator characteristic curve analysis was used to define the glucose value at which an optimal number of macrosomic fetuses could be identified. The test characteristics of sonography in the prediction of macrosomia in the two populations defined by that cut-off value were evaluated.

RESULTS

A glucose level of 120 mg/dL (6.6 mM) was identified as the optimal cutoff for prediction of birth weight > or = 4,000 g. In the group with a glucose level > or = 120 mg/dL, sonographic estimation of fetal weight in the detection of macrosomia offered a sensitivity, specificity, and positive and negative predictive values of 63%, 91%, 71%, and 86%, respectively. In those with glucose level <120 mg/dL, sonography demonstrated a sensitivity, specificity, and positive and negative predictive values of 65%, 89%, 60%, and 91%, respectively.

CONCLUSIONS

In postdates nondiabetic patients, routine glucose challenge testing performed early in pregnancy has limited ability to improve the test characteristics of sonography to predict macrosomia. The positive predictive value of sonographically suspected macrosomia increases from 60-71% in patients whose glucose level was > or = 120 mg/dL (P = 0.002).

Estimation of fetal weight by ultrasound prior to 33 weeks gestation

The aim of this study was to develop an accurate formula for the ultrasonic prediction of fetal weight for infants < 33 weeks gestational age and < or = 1500 g birthweight. The subjects comprised live births free of lethal malformations or chromosomal anomalies, < 33 weeks gestational age and with birthweights +/- 1500 g born in the Royal Women's Hospital between January 1990 and March 1996. All subjects had accurate gestational age confirmed by ultrasound prior to 20 weeks gestation and ultrasound measurements within 72 hours of birth of biparietal diameter (BPD), femur length (FL) and abdominal circumference (AC). A formula with the highest explained variance was computed by linear regression analysis using the three fetal variables in various combinations from 54 infants born between January 1990 and December 1993. The optimal formula was: Log(10)birthweight = 0.714627 + 0.077362.AC + 0.058758.BPD + 0.287037.FL - 0.011274.AC.FL. The new formula was more accurate compared with existing formulae when tested in a separate cohort of 39 infants born between January 1994 and March 1996.

Reference values for differences between cardio-circulatory variables of normal twin fetuses

BACKGROUND

No reference values exist concerning the differences between cardio-circulatory variables of normal twin fetuses. The normal data could be useful in the identification of conditions causing opposite hemodynamic effects on each twin.

OBJECTIVE

To establish the normal differences among cardio-circulatory parameters of twin fetuses during the second and third trimesters of gestation.

MATERIALS AND METHODS

Twenty-seven normal twin pregnancies were used in this longitudinal and prospective study. Doppler-echocardiographic investigations were performed every 2-3 weeks starting at an average of 23.11 +/- 3.13 (mean +/- standard deviation) weeks' gestation. At each visit, the following cardio-circulatory variables were evaluated: the cardio-thoracic ratio, the ventricular wall and septal thicknesses, end-diastolic and systolic diameters, ventricular fractional shortenings, velocity of circumferential fibre shortenings and left and right ventricular outputs. In addition the following measurements were made from Doppler recordings: through both aortic and pulmonary valve the acceleration and ejection times, the peak systolic velocities and the velocity time integrals; and through both mitral and tricuspid valves peak velocities of E and A waves and the E/A ratios. Finally the pulsatility index of the umbilical artery was also evaluated.

RESULTS

There was no single variable where the intertwin difference changed with gestational age. No systematic difference between the smaller and larger twin could be demonstrated for any variables except for the cardio-thoracic ratio.

CONCLUSION

Reference tables should permit a comparative approach between the two twins in the investigation of life threatening complications such as twin-to-twin transfusion syndrome.

Estimation of fetal weight before and after amniotomy in the laboring gravid woman

OBJECTIVE

This study was undertaken to search for differences between fetal weights estimated both ultrasonographically and clinically before and after amniotomy in laboring gravid women.

STUDY DESIGN

Estimates of fetal weight (ultrasonographic and clinical) were obtained for laboring gravid women before and after amniotomy. These estimates were compared with actual birth weights determined post partum.

RESULTS

One hundred sixty-two patients completed the study protocol. Comparisons made with unpaired Student t test analyses demonstrated a difference (P <.001) between ultrasonographically estimated fetal weights before and after amniotomy. Simple regression analysis showed a correlation between both ultrasonographic and clinical estimates of fetal weight and actual birth weights before and after amniotomy, with postamniotomy clinical estimates having the strongest correlation (ultrasonographic preamniotomy estimate, R = 0.717; ultrasonographic postamniotomy estimate, R = 0.630; clinical preamniotomy estimate, R = 0.742; and clinical postamniotomy estimate, R = 0.788). Of all ultrasonographic parameters measured, preamniotomy abdominal circumference correlated best with actual birth weight (R = 0.730).

CONCLUSION

Clinical estimates of fetal weight after amniotomy correlated well with actual birth weights. Preamniotomy abdominal circumference was the ultrasonographic parameter best for prediction of actual birth weight. Maternal weight affected clinical but not ultrasonographic estimates of fetal weight in this study. However, clinical estimates of fetal weight were actually superior to ultrasonographic estimates of fetal weight in this study.

Estimating fetal weight in the management of macrosomia

The purpose of this review is to examine the evidence that, including estimates of fetal macrosomia in patient care, will decrease adverse perinatal outcomes. A literature search for the years 1980 to 1999 was used. Shoulder dystocia and brachial plexus injuries occur more often in macrosomic than in non-macrosomic neonates. However, 26 to 58 percent of shoulder dystocias and 24 to 44 percent of brachial plexus injuries occur to babies weighing less than 4000 gm. Persistence of impairment is extremely rare. Neither historical nor clinical factors have strong positive predictive values for macrosomia. From 15 to 81 percent of the babies predicted to be macrosomic are confirmed by birth weight. Of babies determined to be macrosomic at birth, only 50 to 100 percent were successfully predicted. Shoulder dystocia and brachial plexus injuries are unpredictable events. Available evidence suggests that planned interventions based on estimates of fetal weight do not reduce the incidence of shoulder dystocia and do not decrease adverse outcomes attributable to fetal macrosomia.

Fetal biometry in different ethnic groups

OBJECTIVE

The aim of this study was to determine whether differences in ultrasound-measured fetal biometry exist between pregnant woman of autochthonous Belgian origin and migrant women from Morocco and Turkey.

METHOD

A prospective cross-sectional study was performed in which fetal biparietal diameter, head circumference, abdominal circumference and femur length were measured in pregnant women presenting between 18 and 40 weeks of gestation. Fetal weight was calculated using the formulae by Shepard and Hadlock. Only uncomplicated singleton pregnancies with a certain date of the last menstrual period, confirmed by early ultrasound, were included. The father of the child had to be of the same ethnic origin as the mother. Polynomial regression of the different measurements was performed for women of autochthonous Belgian origin and for migrant women from Morocco and from Turkey.

RESULTS

Singleton fetuses numbering 524 were examined, including 369 Belgian, 78 Moroccan and 77 Turkish. Polynomial regression was performed for the three groups for the biparietal diameter, head circumference, abdominal circumference, femur length and estimated fetal weight. No significant difference between the three different ethnic groups could be demonstrated for the biparietal diameter (P = 0.39). There was a significant difference for the head circumference (P = 0.017), the abdominal circumference (P = 0.0015), the femur length (P = 0.0014) and the estimated fetal weight for both formulae (Shepard P = 0.047; Hadlock P = 0.0006).

CONCLUSION

In this set of cross-sectional data no significant difference for ultrasound-measured fetal biparietal diameter between autochthonous Belgian women and migrant women from Morocco and from Turkey could be demonstrated. Differences do exist for the head circumference, the abdominal circumference, the femur length and the estimated fetal weight. The use of adapted charts of fetal size for pregnant women of Turkish or Moroccan origin should be considered.

Umbilical artery doppler screening for detection of the small fetus in need of antepartum surveillance

OBJECTIVE

Our goal was to test the hypothesis that umbilical artery Doppler velocimetry identifies fetuses who are small for gestational age and in need of antenatal surveillance.

STUDY DESIGN

Three hundred eight fetuses with either an ultrasonographic weight estimate <10th percentile for gestational age or an abdominal circumference <2.5th percentile for gestational age or both of these had an umbilical artery Doppler measurement of the systolic/diastolic ratio. A systolic/diastolic ratio >90th percentile for gestation was considered abnormal. The incidences of a birth weight <10th percentile, fetal distress, and metabolic acidemia were recorded for both groups (normal vs abnormal umbilical artery Doppler).

RESULTS

Only the umbilical artery systolic/diastolic ratio predicted perinatal outcome in the group of fetuses who were presumed to be small for gestational age. Those 138 fetuses with elevated umbilical artery systolic/diastolic ratios had lower umbilical artery and vein pH values at birth (artery, 7.23 +/- 0.08 vs 7.25 +/- 0.1; P <.02; vein, 7.31 +/- 0.01 vs 7.34 +/- 0.09; P =.01), an increased likelihood of fetal distress consistent with chronic hypoxemia (26.3% vs 8.6%; P <.0001), more admissions to the neonatal intensive care unit (40.7% vs 30.7%; P <.005), and a higher incidence of respiratory distress (66% vs 27.3%; P <.03). However, it is important that no fetus with a normal Doppler flow measurement was delivered with a metabolic acidemia associated with chronic hypoxemia. Further, the likelihood of a false-positive diagnosis of intrauterine growth restriction was increased in the group with a normal umbilical artery Doppler resistance.

CONCLUSION

Antenatal surveillance may be unnecessary in fetuses with suspected intrauterine growth restriction if the umbilical artery systolic/diastolic ratio and amniotic fluid volume are normal, because the complications that occur are intrapartum. If these findings are confirmed in prospective trials, the cost implication of reducing the number of antenatal surveillance tests administered in this group of patients is great.

Receiver operating characteristic curves of ultrasonographic estimates of fetal weight for prediction of fetal growth restriction in prolonged pregnancies

OBJECTIVE

Recent studies have documented increased perinatal morbidity and mortality rates in the growth-restricted postterm fetus. Our purpose was to evaluate the receiver operating characteristic curve of ultrasonographically estimated fetal weight as a predictor of fetal growth restriction in prolonged pregnancies.

STUDY DESIGN

Fetal weight was estimated ultrasonographically within 9 days of delivery (mode 1 day) in members of a cohort of 410 patients with prolonged pregnancies (>41 weeks). Estimated fetal weights were compared with birth weights in receiver operating characteristic curve analysis.

RESULTS

The areas under the receiver operating characteristic curves for predicting birth weights <10th percentile (3125 g in this population) and <5th percentile (2930 g in this population) were 0.89 and 0.96, respectively. Both areas were significantly different from an area indicating a useless test. The estimated fetal weight values corresponding to the inflection points for the receiver operating characteristic curves predicting birth weights <10th percentile and <5th percentile were 3370 and 3200 g, respectively. With estimated fetal weight at less than these test cutoff values, the relative risks for a fetus to have a birth weight <10th percentile or <5th percentile were 14.6 (95% confidence interval, 6.25-33.8) and 89.8 (95% confidence interval, 12.1-665), respectively. Analysis of the receiver operating characteristic curves resulted in improved test characteristics relative to using the actual 10th and 5th birth weight percentiles as cutoff values for estimated fetal weight (relative risk of 14.6 vs 9.5 and 89.8 vs 26.0, respectively).

CONCLUSIONS

Ultrasonographic estimation of fetal weight is a useful test for predicting fetal growth restriction in prolonged pregnancies. Future studies should evaluate whether intervention on the basis of this identification results in improved perinatal outcome.

Comprehensive fetal ultrasonographic growth measurements in triplet gestations

OBJECTIVE

Our purpose was to create tables and graphs of ultrasonographically derived fetal growth parameters in longitudinally studied triplet gestations from a single center.

STUDY DESIGN

All triplet pregnancies managed by our division from 1987 through 1998 were identified. All had first-trimester dating sonograms and complete obstetric sonograms obtained by means of 3.5- or 5.0-MHz curvilinear transducers with freeze-freeze capability and on-screen calipers. Sonograms to assess fetal growth were obtained every 2 to 4 weeks, from 16 to 18 weeks' gestation until delivery. Fetal parameters obtained with each sonogram included biparietal diameter; head circumference; bicerebellar diameter; abdominal circumference; femur, humerus, tibia, and fibula lengths; estimated fetal weight; and head circumference/abdominal circumference ratio. Regression analysis was performed with JMP and Cricket Graph software packages, and lines of best fit with 95% confidence intervals were generated.

RESULTS

A total of 443 ultrasonographic examinations were performed for 33 triplet pregnancies (99 fetuses). Each had between 3 and 6 sonograms obtained, all between 16 and 35 weeks' gestation. Scatterplots of each of the fetal growth parameters against gestational age were created with regression lines of best fit and 95% confidence intervals. All growth parameters were dependent on gestational age.

CONCLUSION

A comprehensive set of fetal growth measurements in triplets from the United States is now available and can be used to assess longitudinal fetal growth.

A simple estimated fetal weight equation for fetuses between 24 and 34 weeks of gestation

OBJECTIVE

To develop a mathematical equation that is simple, accurate and easy to use when applied to low-birth weight or preterm fetuses (< 35 weeks) and to assess previous normal ultrasonic fetal weight curves and make a comparison with normal fetal delivery weight curves.

METHOD

In a large teaching hospital, 269 pregnant mothers were identified by the criteria of normalities, such as: well known LMP, regular menstrual cycles, no use of OCP for the last 3 months, no smoking and no history of diabetes. Birth-weight measurements (adjusted for maternal age, baby's sex, parity and week of gestation) were taken immediately after birth.

RESULTS

Mean gestational age and mean birth' weight + S.D. were 29.5 + 3.02 weeks and 1530.238 237.856 g, respectively. With the aid of a scientific calculator the data were analyzed and a simple regression equation has been derived: EFW (kg) = 0.17 (G.A. - 20), S.D. - 235 g (Honarvar's Formula 1).

CONCLUSION

For estimating weights of preterm or low-birth weight fetuses of less than 2500 g, this simple equation appears to be clinically reliable and easy to use and suggests that previous normal ultrasonic fetal weight curves may underestimate or overestimate normal fetal delivery weight between the 24th and 34th week of gestation. Our formula approximates actual birth weight better and recommends Ott's ultrasonic weight curve for Iranian population.

Estimation of fetal weight in twins: a new mathematical model

OBJECTIVES

Evaluation of new mathematical formula (Femur 4) derived from a twin population to estimate fetal weight in twins using ultrasound. Comparison of Femur 4 is with conventional mathematical models.

DESIGN

Retrospective analysis of ultrasonic measurements of 297 twin babies from 24 to 40 weeks of gestation who were born within 10 days of ultrasound examination.

SETTING

Aberdeen Maternity Hospital.

METHODS

With ultrasonic measurements obtained from twin babies, estimated fetal weight was calculated using the mathematical models of Campbell, Shepard and Hadlock. The calculations were repeated for the model of Femur 4. All models were compared against Femur 4.

RESULTS

The coefficient of determination of the linear regression between the actual and predicted weight was highest for Femur 4 (0.852). Femur 4 had the highest proportion of babies with estimated weights within 10% of actual birthweight (71.4%). In babies who weighed between 2000 and 3000 g, Femur 4 had the least systematic and random error of -1.69 and 8.96, respectively. For babies below the 10th centile for weight, Femur 4 had comparable positive and negative predictive values of 76.0% and 92.3%, respectively. Femur 4 was equally poor at predicting growth discordancy with positive and negative predictive values of 70.0% and 86.5% only.

CONCLUSION

Femur 4 requires measurements of femur length and abdominal circumference only, hence avoiding the need to obtain difficult head measurements which is a common problem in twins. It is a good model for estimation of fetal weight in twins. However, prediction of growth discordancy remains problematic.

Inaccuracy of Ballard scores before 28 weeks' gestation. National Institute of Child Health and Human Development Neonatal Research Network

OBJECTIVE

Ballard scores are commonly used to estimate gestational age (GA). The purpose of this study was to determine the accuracy of the New Ballard Score (NBS) for infants <28 weeks GA by accurate menstrual history and to evaluate NBS as an outcome predictor.

METHODS

Infants weighing 401 to 1500 g in 12 National Institute of Child Health and Human Development Neonatal Research Network centers had NBS performed before age 48 hours. Accuracy of NBS estimates of GA was assessed for infants with GA determined by accurate menstrual history. In a larger cohort of infants, NBS was included in regression models of the association of NBS and death, poor outcome, and duration of hospital stay.

RESULTS

At each week from 22 to 28 weeks GA by accurate menstrual history, NBS estimates exceeded GA by dates by 1.3 to 3.3 weeks, and estimates varied widely (range of widths of 95% CIs for the observations, 6.8 to 11.9 weeks). NBS did not contribute significantly to regression models of death, poor outcome, or duration of hospital stay.

CONCLUSIONS

Inaccuracies in GA determined by the NBS should be considered when treating extremely premature infants, particularly in decisions to forego or administer intensive care. Refinement of GA scoring systems is needed to optimize clinical benefit.

Neural-network-based decision making in diagnostic applications

In this article the NN approach for medical decision making was applied for three specific examples. The first example was decision making with single-valued data for IUGR detection. The second example was decision making with double-valued data in prediction of ovulation. The third example was the use of independent NN modules and consensus theory for prediction of ovulation time. The NN approach has superiority over classical statistical approaches for decision making with medical data for the following reasons: 1. It is distribution-free. 2. It captures correlative features and does not need any specific consideration for mutual test dependence. 3. It provides weighted reliability of various tests. 4. It produces fast, accurate results. The statistical decision approach will probably outperform the NN approach in making decisions when an accurate distribution model is provided. However, the NN is proposed as a useful tool to help physicians in decision making and diagnosis of certain symptoms. The capability and performance of this tool has generally been proven in combining mutually dependent medical tests.

Fetal weight estimation and prediction of fetal macrosomia in non-diabetic pregnant women

In the present study we investigated the accuracy of Shepard's formula in the sonographic diagnosis of macrosomic fetus of non-diabetic pregnant women. Three hundred and eighty-one macrosomic and 450 appropriate for gestational age (AGA) fetuses born to non-diabetic mothers between 37-42 weeks of gestation were included in the study. Ultrasonographic fetal weight estimation within two days of delivery was made using Shepard's formula in all patients. The estimated fetal weights were compared with the actual birth weights of the same subjects. We did not observe any macrosomic newborn birth in pregnant women with 3200 g or less fetal weight estimation. However, in patients with 3400-3499 g fetal weight estimation, a statistically significant increase in macrosomic newborn birth was observed. Only 3.2% of newborns having actual birth weights greater than or equal to 4000 g had sonographic birth weight estimation less than 4000 g. Accuracy of weight estimations using the Shepard's formula was found to be low in macrosomic fetus. On the other hand, increased incidence of macrosomic newborn birth was observed in subjects with ultrasonographic fetal weight estimations above 3400 g and this level may be useful as a cut-off value for prediction of macrosomic fetus in non-diabetic pregnant women.

Forty years of obstetric ultrasound 1957-1997: from A-scope to three dimensions

In this article, we record the history of obstetric ultrasound as it developed worldwide in the second half of the twentieth century. The technological advances during this period saw the evolution of equipment from the original adapted metal flaw detectors producing a simple A-scan to the modern, purpose built, real-time colour flow machines with three-dimensional capability (Fig. 1). Clinically, ultrasound began as a research tool, but the poor quality of the images led to the ridicule of many of the early investigators. However, because of their perseverance, ultrasound developed into an imaging modality providing immense diagnostic capabilities and facilitating with precision many invasive procedures, diagnostic and therapeutic, both of which have made significant contributions to patient care. In this history, we recall the people, the personalities, and the problems they encountered during the development of ultrasound and how these problems were resolved, so that ultrasound now is available for use in the care of pregnant women throughout the developed world.

A comparison between ultrasound and clinical methods for predicting fetal weight

Fetal weight prediction by different methods were compared. Those methods were ultrasound fetal weight estimations using Campbell, Warsof and Hadlock equations, and clinical subjective estimation by experienced obstetricians, as well as clinical objective studies (Zayed's equation). We evaluated 523 Jordanian (Arabic) patients in labour. Our results shows that ultrasound equation provides the highest accuracy in predicting fetal weight. In this study Hadlock's equation was more precise than the other equations. There is still a place for clinical fetal weight estimation, especially if objection methods are used.

The fetal-pelvic index has minimal utility in predicting fetal-pelvic disproportion

OBJECTIVE

Our purpose was to evaluate the fetal-pelvic index in our patient population and to determine whether it would be predictive of route of delivery.

STUDY DESIGN

One hundred seventy-six patients with a previous history or clinical findings in the current pregnancy suggestive of fetal-pelvic disproportion participated in this Human Investigation Committee-approved study. All underwent fetal ultrasonographic examinations and modified digital radiography before labor. Fetal head and abdominal circumferences and maternal inlet and midpelvic circumferences were determined, and the fetal-pelvic index was calculated.

RESULTS

Ninety-one patients fulfilled all aspects of the study, including rigorous criteria pertaining to labor management. Thirty of these patients underwent cesarean delivery and 61 were delivered vaginally. The fetal-pelvic index value for the vaginal delivery group was -5.4 +/- 5.3, as opposed to -2.4 +/- 5.8 in the cesarean delivery group (P <.02). Notwithstanding this difference, the fetal-pelvic index had a low overall ability to predict fetal-pelvic disproportion (0.65) and had associated sensitivity and specificity of 0.27 and 0.84, respectively. Predictive thresholds other than zero were tested, but optimal predictive ability, at a fetal-pelvic index cutoff of 2, was only 70% (sensitivity 0.20, specificity 0.95).

CONCLUSION

In our patient population the fetal-pelvic index was only moderately predictive of fetal-pelvic disproportion. Factors other than those assessed by the fetal-pelvic index are probably important in determining the route of delivery. Further studies are indicated.

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.

Vaginal misoprostol for early second-trimester abortion

OBJECTIVES

To demonstrate the effectiveness and safety of misoprostol without the need of postexpulsion systematic curettage in early second-trimester abortions, i.e. at 13-15 weeks' gestation.

METHODS

A group of 151 women, with gestations from 85 to 105 days, received 800 micrograms of vaginal misoprostol every 25 h for a maximum of three doses, without having postexpulsion systematic preventive curettage performed. Outcome measures included successful abortion (complete abortion without requiring a surgical procedure), side-effects, mean expulsion time and mean time of vaginal bleeding.

RESULTS

Complete abortion occurred in 121/151 subjects (80%; 95% confidence interval, 78-87%). The decrease in hemoglobin was statistically significant (p = 0.0001), but without clinical relevance (11.8 mg/dl (SD, 0.9) before treatment and 11.4 mg/dl (SD, 1.0) afterwards. No statistically significant differences were found between the success rate and any of the women's characteristics. Vaginal bleeding lasted 6 +/- 3 days, spotting 6 +/- 3 days, and total bleeding 12 +/- 5 days (median, 11 days; range, 1-29).

CONCLUSIONS

The acceptable expulsion time in 80% of the cases, the fact that postabortion systematic curettage was not needed, the clinically insignificant hemoglobin loss and the abortion rate obtained, show that misoprostol by vaginal administration may be an alternative for interrupting gestation in the early second trimester of pregnancy.

Elective delivery of infants with macrosomia in diabetic women: reduced shoulder dystocia versus increased cesarean deliveries

OBJECTIVE

We sought to test the hypothesis that elective delivery of infants diagnosed with macrosomia by ultrasonographic studies in diabetic women will significantly reduce the rate of shoulder dystocia without significantly increasing cesarean section rate.

STUDY DESIGN

In a prospective study diabetic women with ultrasonographic estimated fetal weight > or = 4250 gm underwent elective cesarean section; women with estimated fetal weight > or = 90th percentile but < 4250 gm underwent induction of labor. Maternal and neonatal outcomes were analyzed and compared for the periods before and after initiation of the protocol.

RESULTS

A total of 2604 diabetic patients were included in this study. The rate of shoulder dystocia was significantly lower after instituting the protocol (2.4% vs 1.1%, odds ratio 2.2). The cesarean section rate increased significantly between the two periods (21.7% vs 25.1%, p < 0.04). Ultrasonography correctly identified the presence or absence of macrosomia in 87% of patients. Only 10.6% of diabetic patients at term required intervention under the protocol (6.8% labor induction, 3.8% elective cesarean section). The rate of shoulder dystocia was 7.4% in macrosomic infants delivered vaginally.

CONCLUSION

An ultrasonographically estimated weight threshold as an indication for elective delivery in diabetic women reduces the rate of shoulder dystocia without a clinically meaningful increase in cesarean section rate. This practice, in conjunction with an intensified management approach to diabetes, improves the outcome of these high-risk women and their infants.

Placental pathophysiology of the twin oligohydramnios-polyhydramnios sequence and the twin-twin transfusion syndrome

Currently accepted sonographic criteria for antenatal diagnosis of twin-twin transfusion (TTT) syndrome include a monochorionic placenta with same-sex twins, marked growth discordance, and oligohydramnios of the growth-retarded twin with coexistent polyhydramnios of the larger twin. Our previous report of nine women fulfilling these criteria, examined using sequential funipuncture of both fetuses, demonstrated inter-twin blood transfusion in only four cases (44 per cent). It was proposed that traditional sonographic criteria actually describe a heterogeneous group of disorders more appropriately described as the twin oligohydramnios-polydramnios sequence (TOPS). True TTT is a subset of this population, the antenatal diagnosis of which requires specific demonstration of transfusion from one fetus (donor) to the other (recipient). In this report, antenatal placental evaluation has been correlated using duplex pulsed-wave Doppler analysis of arterial blood flow velocity with postpartum gross and histopathologic evaluation of the placenta, with special attention to microvasculature. There was a higher incidence of resistance to blood flow, abnormal umbilical cord insertion, and diminished placental microvasculature associated with oligohydramnic growth-retarded (donor) twins when compared with polyhydramnic (recipient) twins. Based on these observations, it is proposed that TTT and TOPS represent asymmetric placental insufficiency resulting from aberrant placentation.