Prediction of fetal macrosomia using humeral soft tissue thickness

Fasting plasma glucose and fetal ultrasound predict the occurrence of neonatal macrosomia in gestational diabetes mellitus

OBJECTIVE

The cause of fetal overgrowth during pregnancy is still unclear. This study aimed to analyze and predict the risk of macrosomia in pregnant women with gestational diabetes mellitus (GDM).

METHODS

This study was a retrospective study collected from October 2020 to October 2021. A total of 6072 pregnant women with a routine 75-g oral glucose tolerance test (OGTT) during 24-28 gestational weeks were screened. Nearly equal numbers of pregnant women with gestational diabetes and with normal glucose tolerance (NGT) were included in the study. Multivariate logistic regression analysis and receiver operating characteristic (ROC) curve were performed to determine the index and inflection point for predicting macrosomia occurrence.

RESULTS

The data of perinatal outcomes of 322 GDM and 353 NGT who had given birth to single live babies at term were analyzed. We found that significant cut-off values for the prediction of macrosomia are 5.13mmol/L in fasting plasma glucose (FPG), 12.25kg in gestational weight gain (GWG), 3,605g in ultrasound fetal weight gain (FWG) and 124mm in amniotic fluid index (AFI).The area under the ROC curve of this predictive model combined all variables reached 0.953 (95% CI: 0.914 ~ 0.993) with a sensitivity of 95.0% and a specificity of 85.4%.

CONCLUSIONS

FPG is positively associated with newborn birth weight. An early intervention to prevent macrosomia may be possible by combining maternal GWG, FPG, FWG, and AFI in gestational diabetes.

Ultrasound evaluation of the fetal fat tissue, heart, liver and umbilical cord measurements in pregnancies complicated by gestational and type 1 diabetes mellitus: potential application in the fetal birth-weight estimation and prediction of the fetal macrosomia

BACKGROUND

The aim of the study was to evaluate the ultrasound-derived measurements of the fetal soft-tissue, heart, liver and umbilical cord in pregnancies complicated by gestational (GDM) and type 1 diabetes mellitus (T1DM), and further to assess their applicability in the estimation of the fetal birth-weight and prediction of fetal macrosomia.

METHODS

Measurements were obtained from diet-controlled GDM (GDMG1) (n = 40), insulin-controlled GDM (GDMG2) (n = 40), T1DM (n = 24) and healthy control (n = 40) patients. The following parameters were selected for analysis: fetal sub-scapular fat mass (SSFM), abdominal fat mass (AFM), mid-thigh fat/lean mass (MTFM/MTLM) and inter-ventricular septum (IVS) thicknesses, heart and thorax circumference and area (HeC/HeA; ThC/ThA), liver length (LL), umbilical cord/vein/arteries circumference and area (UmC/UmA; UvC/UvA; UaC/UaA) together with total umbilical vessels (UveA) and Wharton's jelly area (WjA). Regression models were created in order to assess the contribution of selected parameters to fetal birth-weight (FBW) and risk of fetal macrosomia.

RESULTS

Measurements of the fetal SSFM, AFM, MTFM, MTFM/MTLM ratio, HeC, HeA, IVS, LL, UmC, UmA, UaC, UaA, UveA and WjA were significantly increased among patients with GDMG2/T1DM as compared to GDMG1 and/or control groups (p < .05). The regression analysis revealed that maternal height as well as fetal biparietal diameter, abdominal circumference (AC), AFM and LL measurements were independent predictors of the FBW (p < .05). In addition, increase in the fetal AFM, AC and femur length (FL) was associated with a significant risk of fetal macrosomia occurrence (p < .05). The equation developed for the FBW estimation [FBW(g) = - 2254,942 + 17,204 * FL (mm) + 105,531 * AC (cm) + 131,347 * AFM (mm)] provided significantly lower mean absolute percent error than standard formula in the sub-group of women with T1DM (5.7% vs 9.4%, p < .05). Moreover, new equation including AC, FL and AFM parameters yielded sensitivity of 93.8%, specificity 77.7%, positive predictive value 54.5% and negative predictive value of 97.8% in the prediction of fetal macrosomia.

CONCLUSIONS

Ultrasound measurements of the fetal soft tissue, heart, liver and umbilical cord are significantly increased among women with GDM treated with insulin and T1DM. In addition to standard biometric measurements, parameters, such as AFM, may find application in the management of diabetes-complicated pregnancies.

Identification of large-for-gestational age fetuses using antenatal customized fetal growth charts: Can we improve the prediction of abnormal labor course?

INTRODUCTION

Fetal overgrowth is an acknowledged risk factor for abnormal labor course and maternal and perinatal complications. The objective of this study was to evaluate whether the use of antenatal ultrasound-based customized fetal growth charts in fetuses at risk for large-for-gestational age (LGA) allows a better identification of cases undergoing caesarean section due to intrapartum dystocia.

MATERIAL AND METHODS

An observational study involving four Italian tertiary centers was carried out. Women referred to a dedicated antenatal clinic between 35 and 38 weeks due to an increased risk of having an LGA fetus at birth were prospectively selected for the study purpose. The fetal measurements obtained and used for the estimation of the fetal size were biparietal diameter, head circumference, abdominal circumference and femur length, were prospectively collected. LGA fetuses were defined by estimated fetal weight (EFW) >95th centile either using the standard charts implemented by the World Health Organization (WHO) or the customized fetal growth charts previously published by our group. Patients scheduled for elective caesarean section (CS) or for elective induction for suspected fetal macrosomia or submitted to CS or vacuum extraction (VE) purely due to suspected intrapartum distress were excluded. The incidence of CS due to labor dystocia was compared between fetuses with EFW >95th centile according WHO or customized antenatal growth charts.

RESULTS

Overall, 814 women were eligible, however 562 were considered for the data analysis following the evaluation of the exclusion criteria. Vaginal delivery occurred in 466 (82.9 %) women (435 (77.4 %) spontaneous vaginal delivery and 31 (5.5 %) VE) while 96 had CS. The EFW was >95th centile in 194 (34.5 %) fetuses according to WHO growth charts and in 190 (33.8 %) by customized growth charts, respectively. CS due to dystocia occurred in 43 (22.2 %) women with LGA fetuses defined by WHO curves and in 39 (20.5 %) women with LGA defined by customized growth charts (p 0.70). WHO curves showed 57 % sensitivity, 72 % specificity, 24 % PPV and 91 % NPV, while customized curves showed 52 % sensitivity, 73 % specificity, 23 % PPV and 91 % NPV for CS due to labor dystocia.

CONCLUSIONS

The use of antenatal ultrasound-based customized growth charts does not allow a better identification of fetuses at risk of CS due to intrapartum dystocia.

The Use of Ultrasound to Identify Fetuses with Macrosoomia in Diabetic Pregnancies

Diabetic pregnancies are associated with an increased incidence of fetal macrosomia. Prenatal detection of macrosomia is particularly important because of the potential maternal and neonatal morbidity associated with vaginal delivery. Early detection of macrosomia enables the clinician to decease the risk of morbidityeby either fprearing for complications associated with vaginal delivery or changing the timing or route of delivery. M acrosomia is suspected with an estimated faetalweight greate than or eqal to 4,000 g. Two; methods are:used to predict: fetal birth weight The first method is clinical evaluation,:which is based on abdominal palpation of fetal parts and fundatl: size. AThe second metho dis by sonogr aphic examinanon, which is based onfetal biparietal' diameter, abdominal circumferee, and femur length, which are then. plugged into a regression equation to calculat fetal: weight. Clinical techn ques do not relably predict fetal weight. Although ultrasound i's not particularly accurate at determining fetal wiht, it is more reliable than cliniali technique. Ultrasound therefore plays a major role in i;early detectio of m acrsoma. Current research valuates altering or Oexpandingthe use of ultrasound to more accurately-predict macrosomia in infants of diabetic mothers.

Fetal weight estimation in gestational diabetic pregnancies: comparison between conventional and three-dimensional fractional thigh volume methods using gestation-adjusted projection

OBJECTIVES

To evaluate the accuracy of gestation-adjusted birth-weight estimation using a three-dimensional (3D) fractional thigh volume (TVol) method in pregnant women with gestational diabetes mellitus (GDM), and to compare it with the conventional two-dimensional method of Hadlock et al.

METHODS

Pregnant women with GDM were referred at 34 to 36 + 6 weeks' gestation for ultrasound examination. Estimated fetal weight (EFW) was obtained using both the Hadlock and the TVol methods. Using a gestation-adjusted projection method, predicted birth weight was compared to actual birth weight at delivery.

RESULTS

Based on 125 pregnancies, the TVol method with gestation-adjusted projection had a mean (± SD) percentage error in estimating birth weight of -0.01 ± 5.0 (95% CI, -0.96 to 0.98)% while the method of Hadlock with gestation-adjusted projection had an error of 1.28 ± 9.1 (95% CI, -0.33 to 2.87)%. The mean percentage error of the two methods was significantly different (P = 0.039), while the random error was not (P = 1.0). For the prediction of macrosomia (birth weight ≥ 4000 g, n = 19), sensitivity was 84 and 63% for the TVol and Hadlock methods, respectively (95% CI for difference -2 to 44%, P = 0.22) and specificity was 96 and 89% for the TVol and Hadlock methods, respectively (95% CI for difference 5-9%, P = 0.01).

CONCLUSIONS

In women with GDM, a new method of estimating birth weight based on 3D-TVol measurements performed at 34 + 0 to 36 + 6 weeks' gestation and gestation-adjusted projection of estimated fetal weight, is more accurate than the standard method based on Hadlock's formula in predicting birth weight. The TVol method has comparable sensitivity but higher specificity than the Hadlock method in predicting neonatal macrosomia.

Does use of a sex-specific model improve the accuracy of sonographic weight estimation?

OBJECTIVE

To determine whether the use of a sex-specific sonographic model improves the accuracy of fetal weight estimation.

METHODS

New regression models (sex-independent and sex-specific) were developed, based on 1708 sonographic weight estimations performed within 3 days prior to delivery. The accuracy of these models was compared to that of several published models including two of the original Hadlock models (which incorporate the biometric indices abdominal circumference (AC), biparietal diameter (BPD), femur diaphysis length (FL) and head circumference (HC) as follows: AC-FL-BPD and AC-FL-HC, designated here as Hadlock I and Hadlock II, respectively), modified versions of the Hadlock I and II models for which coefficients were adjusted to our local cohort, sex-specific versions of the Hadlock I and II models and Schild's model (a previously published sex-specific model).

RESULTS

The unadjusted models of Hadlock and Schild were associated with the highest systematic error (1.6-4.9%; P < 0.001) which was significantly higher for females (2.3-4.9%) compared to males (1.6-2.0%; P < 0.001). Adjustment of model coefficients to the local population decreased the systematic error (-1.4% to 1.5%) and resulted in a systematic error that was of similar magnitude (P = 0.3) but opposite in direction for male and female fetuses. The sex-specific models (adjusted or newly developed) were associated with the lowest systematic error (-0.4 to 0.5%) and were the only models for which the systematic error was similar for male and female fetuses. There were no differences in the systematic error between adjusted sex-specific versions of the Hadlock I and II models and the newly developed sex-specific models (0.0% to 0.4% vs. - 0.4% to 0.5%; P = 0.4). The random error was similar for all models and, for most of the models, was unrelated to fetal sex.

CONCLUSIONS

The use of sex-specific models appears to improve the accuracy of fetal weight estimation, principally because the optimal set of model coefficients differs for male and female fetuses. The improved accuracy is mainly the result of a decrease in systematic error, as the random error was not affected by the use of such sex-specific models.

Ultrasonographic weight estimation in large for gestational age fetuses: a comparison of 17 sonographic formulas and four models algorithms

OBJECTIVE

To evaluate the accuracy of different formulas and role of fetal parameters (cephalic, abdominal, femur) used for estimation fetal weight (EFW) in large for gestational age (LGA) fetus in diabetic and non-diabetic mothers.

METHODS

Seventeen formulas were assessed individually and clustered in four algorithms (X, Y, Z, W) on the basis of fetal biometric parameters using the mean absolute % error, standard deviation (SD), prediction within +/-5%, +/-10%, +/-15% of error and introducing new variable hypotenuse test (HPT) that can sum up precision and accuracy of formulas employed. For predicting fetal macrosomia (BW > or = 4200 g) a receiver-operating characteristic curve was constructed.

RESULTS

Warsof2 formula showed the lowest mean % error, SD and HPT (p < 0.01) with overall prediction +/-5, +/-10%, +/-15% of birth weight in 68, 94 and 98%. The formulas that were only based on abdominal measurement (Warsof2, Hadlock1, Campbell) showed the best ability to identify fetal macrosomia. The X algorithm confirming primary role of abdominal circumference for EFW in diabetic mothers.

CONCLUSIONS

Accuracy of EFW in LGA fetuses is attributable to the biometric parameters used. Our findings show that the best formulas for EFW are those which only consider the abdominal measurements, especially in diabetic mothers. The new variable that we propose (HPT) confirms this result.

Growth of fetal lean mass and fetal fat mass in gestational diabetes

OBJECTIVES

This study was carried out to investigate growth indicators of fetal lean mass and fat mass in the second half of the gestational period in pregnancies complicated by gestational diabetes mellitus (GDM) in comparison to normal control pregnancies.

METHODS

Forty-three control and 171 GDM pregnancies were followed longitudinally by ultrasound examinations, measuring both traditional biometric parameters and six non-traditional parameters for the evaluation of lean and fat mass. A mixed linear model derived from the log-Count function was used to model fetal growth and to make comparisons between groups. Factor analysis was used to evaluate the associations between gestational diabetes and fetal size and fetal fat/lean mass ratios.

RESULTS

A total of 506 scans were obtained in the 214 pregnancies, a mean of 2.4 scans per pregnancy (range 2-5). Maternal age, prepregnancy weight and body mass index were significantly higher in GDM pregnancies. Fetuses of GDM pregnancies showed greater growth, at the same gestational age, for each lean and fat non-traditional parameter, having a significantly greater amount of total tissue mass and a higher fat mass/lean mass ratio, independent of gestational age, in comparison to control pregnancies.

CONCLUSIONS

A non-invasive, repeatable evaluation of fetal body composition in utero could represent a useful method for the early detection of growth abnormalities and for direct estimation of the fetal metabolic status.

Defining normal and abnormal fetal growth: promises and challenges

Normal fetal growth is a critical component of a healthy pregnancy and influences the long-term health of the offspring. However, defining normal and abnormal fetal growth has been a long-standing challenge in clinical practice and research. We review various references and standards that are used widely to evaluate fetal growth and discuss common pitfalls of current definitions of abnormal fetal growth. Pros and cons of different approaches to customize fetal growth standards are described. We further discuss recent advances toward an integrated definition for fetal growth restriction. Such a definition may incorporate fetal size with the status of placental health that is measured by maternal and fetal Doppler velocimetry and biomarkers, biophysical findings, and genetics. Although the concept of an integrated definition appears promising, further development and testing are required. An improved definition of abnormal fetal growth should benefit both research and clinical practice.

Macrosomia: a new formula for optimized fetal weight estimation

OBJECTIVES

To develop and test a specific formula for estimating weight in the macrosomic fetus.

METHODS

Ultrasound estimations of fetal weight were carried out within 1 week of delivery in 424 singleton fetuses with a birth weight of > or = 4000 g. Exclusion criteria were multiple pregnancy, intrauterine death and major structural or chromosomal anomalies. Stepwise regression modeling was used to derive a prediction formula with birth weight as the dependent variable and maternal booking weight and fetal biometric measurements as independent parameters. After a new formula for estimated fetal weight (EFW) had been developed in a formula-finding group (n = 284), it was compared with commonly used weight equations (evaluation group, n = 140).

RESULTS

The new formula (log(e)EFW = 7.6377445039 + 0.0002951035 x maternal weight + 0.0003949464 x head circumference + 0.0005241529 x abdominal circumference + 0.0048698624 x femur length) proved to be superior to established equations, with the smallest mean error (mean +/- SD, -10 +/- 202 g), the smallest mean percentage error (mean +/- SD, -0.03 +/- 4.6%) and the lowest mean absolute percentage error (3.69 (range, 0.05-13.57)%) when studied in the evaluation group. With the new formula, 77.9% of estimates fell within +/- 5% of the actual weight at birth, 97.1% within +/- 10%, and 100% within +/- 15% and +/- 20%.

CONCLUSIONS

The new formula allows better weight estimation in the macrosomic fetus.

Non-diabetic macrosomia: an obstetric dilemma

Fetal macrosomia represents a continuing challenge in obstetrics, as it has risk of shoulder dystocia leading to transient or permanent fetal, maternal injury and medicolegal liability. The overall incidence of macrosomia has been rising. Non-diabetic macrosomia is still an obstetric dilemma, as there is no clear consensus regarding its ante-partum prediction and management, as accurate diagnosis is only made retrospectively. The risk of shoulder dystocia rises from 1.4% for all vaginal deliveries to 9.2-24% for birth weights more than 4,500 g. Unfortunately, 50% of all cases of shoulder dystocia occur at birth weights of less than 4,000 g. Brachial plexus injury occurs in 1:1,000 births and permanent damage in 1:10,000 deliveries (12% of all) leading to litigation 1:45,000 deliveries. The prenatal diagnosis of macrosomia remains imprecise. Pre-pregnancy and ante-partum risk factors and ultrasound have poor predictive value. Induction of labour and prophylactic caesarean delivery has not been shown to alter the incidence of shoulder dystocia among nondiabetic patients. Caesarean section and induction of labour are associated with increased risk of operative morbidity and mortality with added cost implications.

Weight estimation by three-dimensional ultrasound imaging in the small fetus

OBJECTIVES

To improve birth weight estimation in fetuses weighing <or= 1600 g at birth by deriving a new formula including measurements obtained using three-dimensional (3D) sonography.

METHODS

In a prospective cohort study, biometric data of 150 singleton fetuses weighing <or= 1600 g at birth were obtained by sonographic examination within 1 week before delivery. Exclusion criteria were multiple pregnancy, intrauterine death as well as major structural or chromosomal anomalies. A new formula was derived using our data, and was then compared with currently available equations for estimating weight in the preterm fetus.

RESULTS

Different statistical estimation strategies were pursued. Gradient boosting with component- wise smoothing splines achieved the best results. The resulting new formula (estimated fetal weight = 656.41 + 1.8321 x volABDO + 31.1981 x HC + 5.7787 x volFEM + 73.5214 x FL + 8.3009 x AC - 449.8863 x BPD + 32.5340 x BPD(2), where volABDO is abdominal volume determined by 3D volumetry, HC is head circumference, volFEM is thigh volume determined by 3D volumetry, FL is femur length and BPD is biparietal diameter) proved to be superior to established equations in terms of mean squared prediction errors, signed percentage errors and absolute percentage errors.

CONCLUSIONS

Our new formula is relatively easy to use and needs no adjustment to weight percentiles or to fetal lie. In fetuses weighing <or= 1600 g at birth it is superior to weight estimation by traditional formulae using two-dimensional measurements.

Reproducibility of sonographic assessment of fetal liver length in diabetic pregnancies

OBJECTIVES

Assessing fetal liver size might be useful in monitoring the effectiveness of the treatment of diabetes in pregnancy. We aimed to assess the reproducibility of fetal liver-length measurement in pregnant women with diabetes.

METHODS

From 3 April 2006 to 5 December 2006, we assessed intraobserver and interobserver variation of fetal liver-length measurements on 55 sonograms in 44 pregnant women with diabetes, 34 of whom had gestational diabetes. The mean maternal age was 33 years, the mean maternal weight was 92 kg and the mean body mass index (BMI) was 33.7 kg/m(-2). The effect of covariates BMI, gestational age and maternal age on the reproducibility of fetal liver length was assessed by calculating intraobserver SD ratios. We compared liver length with abdominal circumference and gestational age. Nine of 12 sonographers scanned, on average, six women (range, 3-12) as the first sonographer, and all 12 sonographers scanned, on average, four women (range, 1-10) as the second sonographer. The data were analyzed using a hierarchical linear model.

RESULTS

Measurement of fetal liver length was reproducible. The intraobserver SD was 3.06 (95% CI, 2.68-3.59) mm; the interobserver SD was 2.17 (95% CI, 0.59-4.83) mm; the intraobserver correlation was 0.77 (95% CI, 0.63-0.87), and the interobserver correlation was 0.84 (95% CI, 0.51-0.99). The covariate effects were minimal, the SD for a 1-unit increase in the covariate was 1.06 for gestational age, 0.98 for BMI, and 0.97 for maternal age.

CONCLUSIONS

Measurement of fetal liver length in the diabetic pregnancy is reproducible. It is worthy of further investigation as a parameter for monitoring the effectiveness of treatment of the diabetic pregnancy.

Estimation of fetal weight by measurement of fetal thigh soft-tissue thickness in the late third trimester

OBJECTIVE

The accuracy of current formulae for the sonographic estimation of fetal weight (EFW) is compromised by significant intra- and interobserver variability of biometrical measurements, particularly circumferences. The aim of this study was to assess the reliability of the linear measurement of mid-thigh soft-tissue thickness (STT) and to derive a novel formula for EFW.

METHODS

This was a prospective study involving 388 singleton uncomplicated pregnancies. There were three consecutive phases: (1) to verify the relationship between STT and birth weight, (2) to derive a novel formula for EFW using femur length and STT only, and (3) to test the accuracy of the new equation. Only the 290 patients who delivered within 48 h of measurement were considered for the analysis. A comparison with other formulae was performed.

RESULTS

STT was significantly correlated with both abdominal circumference and birth weight (r(2) = 0.36 and 0.46, respectively; P < 0.001). Both intra- and interobserver variability were satisfactory (0.44 +/- 0.27 and 0.57 +/- 0.35 mm, respectively). The equation for EFW was developed using multiple stepwise regression analysis (EFW = - 1687.47 + (54.1 x femur length) + (76.68 x STT)) and tested prospectively on 69 patients. The new formula yielded results (r = 0.79) that were slightly better in accuracy than two other published equations, and had an absolute mean error of < 15% in 97% of cases.

CONCLUSIONS

Our findings confirm the potential of the linear measurement of mid-thigh STT as a valuable parameter for the sonographic assessment of fetal growth and EFW. Our new equation is apparently at least as reliable as the most widely used formulae for EFW.

Large cross-sectional area of the umbilical cord as a predictor of fetal macrosomia

OBJECTIVE

To determine whether a large cross-sectional area of the umbilical cord is a predictor of fetal macrosomia.

METHODS

Consecutive patients of > 34 weeks' gestation, who presented for sonographic examination and who delivered within 4 weeks of the examination, were included in the study. The sonographic cross-sectional areas of the umbilical cord, the umbilical vessels and the Wharton's jelly were measured in a free loop of the umbilical cord. Logistic regression analysis was used to determine significant predictors of macrosomia (actual birth weight > 4000 g and > 4500 g). Fetal biometric parameters (biparietal diameter, abdominal circumference and femur length), sonographic estimated fetal weight and umbilical cord area > 95(th) centile for gestational age were used as covariates.

RESULTS

During the study period, 1026 patients were enrolled. Fifty-three (5.2%) newborns had a birth weight > 4000 g, and 22 (2.1%) weighed > 4500 g. The proportion of cases with a large umbilical cord was significantly higher in the group of macrosomic compared with non-macrosomic infants (54.7% vs. 8.7%, P < 0.0001). Multiple regression models demonstrated an independent contribution of the large cord in the prediction of birth weight > 4000 g and > 4500 g (odds ratio (95% CI), 20.6 (9.2-45.9) and 4.2 (1.2-17.7), respectively). The sensitivity, specificity and positive and negative predictive values of a sonographic large umbilical cord were 54.7%, 91.3%, 25.4%, and 97.4%, respectively. The combination of abdominal circumference > 95(th) centile and large cord predicted 100% of macrosomic infants. The proportion of umbilical cords with a Wharton's jelly area > 95(th) centile for gestation was significantly higher in macrosomic fetuses of diabetic compared with non-diabetic mothers.

CONCLUSIONS

Sonographic assessment of umbilical cord area may improve the prediction of fetal macrosomia.

Detection and prevention of macrosomia

It is overly simplistic to try to identify optimal glycemic thresholds, fetal growth characteristics, and methods of detection in the prevention of fetal overgrowth and its attendant morbidities that can be applied to all pregnancies. We can only hope that, as our understanding of the pathophysiology of diabetes in pregnancy grows, we can "fine-tune" our therapy and surveillance to meet the needs of an individual woman who has diabetes and her fetus.

Suspicion and treatment of the macrosomic fetus: a review

OBJECTIVE

To review the prevalence of and our ability to identify macrosomic (birthweight >4000 g) fetuses. Additionally, based on the current evidence, propose an algorithm for treatment of suspected macrosomia.

STUDY DESIGN

A review.

RESULTS

According to the National Vital Statistics, in the United States, the prevalence of newborns weighing at least 4000 g has decreased by 10% in seven years (10.2% in 1996 and 9.2% in 2002) and 19% for newborns with weights >5000 g (0.16% and 0.13%, respectively). Bayesian calculations indicates that the posttest probability of detecting a macrosomic fetus in an uncomplicated pregnancy is variable, ranging from 15% to 79% with sonographic estimates of birth weight, and 40 to 52% with clinical estimates. Among diabetic patients the post-test probability of identifying a newborn weighing >4000 g clinically and sonographically is over 60%. Among uncomplicated pregnancies, there is sufficient evidence that suspected macrosomia is not an indication for induction or for primary cesarean delivery. For pregnancies complicated by diabetes, with a prior cesarean delivery or shoulder dystocia, delivery of a macrosomic fetus increases the rate of complications, but there is insufficient evidence about the threshold of estimated fetal weight that should prompt cesarean delivery.

CONCLUSION

Due to the inaccuracies, among uncomplicated pregnancies suspicion of macrosomia is not an indication for induction or for primary cesarean delivery.

The ultrasound assessment of adipose tissue deposition in fetuses of "well controlled" insulin-dependent diabetic pregnancies

OBJECTIVE

To assess differences in adipose deposition in fetuses from normal pregnancies and women with diabetes.

RESEARCH DESIGN AND METHODS

The study group consisted of 15 well controlled insulin-dependent women with diabetes and 16 controls with a normal glucose. Ultrasound measurements were taken of subcuticular tissue thickness at the abdominal and suprascapular level at 31 and 37 weeks gestation. Triceps and subscapular skinfold thickness were also measured at birth.

RESULTS

Gestational age at delivery and birthweights were not significantly different. At 31 weeks, fasting glucose levels were 5.0 +/- 1 mmol/l for diabetic vs. 3.3 +/- 0.3 mmol/l for controls (P < 0.01), post-prandial 5.6 +/- 0.4 vs. 5.1 +/- 0.3 mmol/l (P < 0.01). At 37 weeks, they were 4.6 +/- 0.2 mmol/l vs. 3.8 +/- 1.1 mmol/l (P < 0.01) and 6.0 +/- 0.6 mmol/l vs. 5.3 +/- 0.3 mmol/l (P < 0.01). Abdominal and suprascapular subcuticular thickness were 4.4 +/- 0.1 mm vs. 3.7 +/- 0.1 mm (P < 0.05) and 4.3 +/- 0.2 mm vs. 3.5 +/- 0.2 mm (P < 0.05) at 31; 5.6 +/- 0.2 mm vs. 4.8 +/- 0.1 mm (P < 0.05) and 5.4 +/- 0.2 mm vs. 4.4 +/- 0.1 mm (P < 0.05) at 37 weeks. At birth, triceps and suprascapular skinfolds were 4.7 +/- 0.1 mm vs. 4.1 +/- 0.1 mm (P < 0.05) and 4.7 +/- 0.2 mm vs. 3.8 +/- 0.1 mm (P < 0.01).

CONCLUSION

Adipose tissue disposition is increased in fetuses of women with well-controlled diabetes. This may be a reflection of higher maternal glucose levels in these women and may explain why even well-controlled diabetic pregnancies are at risk of macrosomia.

A novel ultrasound indentation system for measuring biomechanical properties of in vivo soft tissue

Technologies for soft tissue analysis are advancing at a rapid place. For instance, elastography, which provides soft tissue strain images, is starting to be tried in clinical practice as a tool for diagnosing cancer. Soft tissue deformation modeling and analysis is also an active area of research that has application in surgery planning and treatment. Typically, quantitative soft tissue analysis uses nominal values of soft tissue biomechanical properties. However, in practice, soft tissue properties can vary significantly between individuals. Hence, for soft tissue methodologies to reach their full potential as patient-specific techniques, there is a need to develop ways to efficiently measure soft tissue mechanical properties in vivo. This paper describes a prototype real-time ultrasound (US) indentation test system developed to meet this need. The system is based on the integration of a force sensor and an optical tracking system with a commercial US machine integrated with a suite of analysis methodologies. In a study on a single-layer phantom, we used the system to compare various methods of estimating linear elastic properties (via a theoretical approximation, 2-D finite element analysis, 3-D finite element analysis and a standard material-testing method). In a second study on a three-layer gelatin phantom, we describe a new finite-element-based inverse solution for recovering the Young's moduli of each layer to show how the system can estimate properties of internal components of soft tissue. Finally, we show how the system can be used to derive a modified quasilinear viscoelastic (QVL) model on real breast tissue.

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.

Sonographic estimation of fetal weight in macrosomic fetuses: diabetic versus non-diabetic pregnancies

The objective of this study is to compare the accuracy of sonographic estimation of fetal weight of macrosomic babies in diabetic vs non-diabetic pregnancies. All babies weighing 4,000 g or more at birth, and who had ultrasound scans performed within one week of delivery were included in this retrospective study Pregnancies with diabetes mellitus were compared to those without diabetes mellitus. The mean simple error (actual birthweight--estimated fetal weight); mean standardised absolute error (absolute value of simple error (g)/actual birthweight (kg)); and the percentage of estimated birthweight falling within 15% of the actual birthweight between the two groups were compared. There were 9,516 deliveries during the study period. Of this total 1,211 (12.7%) babies weighed 4,000 g or more. A total of 56 non-diabetic pregnancies and 19 diabetic pregnancies were compared. The average sonographic estimation of fetal weight in diabetic pregnancies was 8% less than the actual birthweight, compared to 0.2% in the non-diabetic group (p < 0.01). The estimated fetal weight was within 15% of the birthweight in 74% of the diabetic pregnancies, compared to 93% of the non-diabetic pregnancies (p < 0.05). In the diabetic group, 26.3 % of the birthweights were underestimated by more than 15 %, compared to 5.4% in the non-diabetic group (p < 0.05). In conclusion, the prediction accuracy of fetal weight estimation using standard formulae in macrosomic fetuses is significantly worse in diabetic pregnancies compared to non-diabetic pregnancies. When sonographic fetal weight estimation is used to influence the mode of delivery for diabetic women, a more conservative cut-off needs to be considered.

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.

Sonographic and clinical methods in the diagnosis of macrosomia

Receiver operator characteristic curves for both clinical and sonographic predictions of macrosomia subsume areas between 0.81 and 0.95, significantly larger than the area of 0.5 that indicates a useless test. Thus, these tests are defined as useful from a statistical point of view. Prediction of macrosomia by clinical or imaging techniques, however, is limited by the substantial false-positive and false-negative rates inherent in these tests. We recommend that physicians continue to use clinical methods to estimate fetal weight, including asking women with parity to provide their own estimates. We recognize that the relative error associated with clinical or sonographic estimates of fetal weight limits their use in clinical practice. Sonographic laboratories may improve their results by performing ROC curve analysis on their own data and by selecting cutoff values that best predict macrosomia in their setting. Serial sonographic measurements that are above the limits chosen to define macrosomia increase the likelihood that a birth weight will be macrosomic. Separate ROC curves must be generated for twins and breech presentations and for patients with diabetes to answer weight-related clinical questions such as mode and timing of delivery. Three-dimensional ultrasound and magnetic resonance imaging are expected to generate ROC curves for estimates of fetal weight that are better than those for two-dimensional ultrasound or clinical estimates. Such analyses have yet to be published.

Correctly identifying the macrosomic fetus: improving ultrasonography-based prediction

OBJECTIVE

Our goal was to improve the accuracy of estimating fetal weights among macrosomic fetuses with the traditional measurements of abdominal circumference, femur length, and head circumference.

STUDY DESIGN

We used 4831 cases without anomalies from an ultrasonography laboratory database with an estimated fetal weight obtained a maximum of 14 days before delivery. Abdominal circumference, femur length, and head circumference were each regressed on birth weight to obtain estimated fetal weight by abdominal circumference, femur length, and head circumference, respectively. We compared the individual variation for estimated fetal weight by abdominal circumference, femur length, and head circumference by calculating a within-subject standard deviation to quantify the level of disparity. We adjusted the estimated fetal weight to the date of delivery and for dependencies on maternal diabetes mellitus, weight, and height. We then weighted cases with birth weight >4500 g and diabetic cases with birth weight >4000 g 20-fold (weighted estimated fetal weight) for the purpose of creating a favorable bias for classifying these cases. The equation of Hadlock et al, with abdominal circumference, femur length, and head circumference, was applied as a benchmark estimated fetal weight.

RESULTS

Of the 4831 newborns, 308 (6.4%) had a birth weight >4000 g, and 56 (1.2%) had a birth weight >4500 g. There were 154 pregnancies complicated by diabetes mellitus; 26 (16.9%) of the resulting infants weighed >4000 g, and 5 (3.2%) weighed >4500 g. At 95% specificity, the weighted estimated fetal weight had a sensitivity of 85.7% at a cut point of 3912 g, compared with a sensitivity of 71.4% at 3604 g by use of the estimated fetal weight of Hadlock et al.

CONCLUSIONS

We were able to improve the accuracy of identifying the macrosomic fetus compared to reliance on the equation by Hadlock et al. A fetus was found to be at significantly increased risk for birth weight >4000 g when the estimated fetal weight based on abdominal circumference is larger than that based on either head circumference or femur length or when there is a large within-subject variance in estimated fetal weight based on abdominal circumference, femur length, and head circumference. We also found that there were significantly different groups of patients whose estimated fetal weights require different equations for better estimates. Even given ultrasonographic measurements, taking into account maternal height, weight, and presence of diabetes mellitus can improve macrosomia detection. Although these findings remain to be optimized and validated, the approach used here appears to yield better predictions than the current "one function fits all" approach.

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.

Prenatal diagnosis of macrosomia in pregnancy complicated by diabetes mellitus

OBJECTIVE

To provide a concise review of current practices regarding prenatal diagnosis of excess fetal growth in pregnancies complicated by diabetes mellitus.

METHODS

A literature review of relevant publications.

RESULTS

Sonographic estimation of fetal size at term is frequently undertaken in the management of diabetic pregnancy. Considerable error in fetal weight estimations, particularly in asymmetrically enlarged fetuses, may limit the accuracy and clinical utility of these measurements.

CONCLUSIONS

The limitations and potential inaccuracy of current sonographic methods to detect the large-for-gestational age fetus of a diabetic mother are acknowledged. Customized formulae are of limited benefit so that further study of techniques aimed at assessing fetal fat content and distribution should be undertaken. These methods may improve detection of the large fetus and aid in clinical decision making.

Fetal growth in diabetic pregnancy

In summary, fetal macrosomia occurs in almost one third of diabetic pregnancies regardless of class. Abnormal fetal fat stores lead to difficult labor, dystocia, and birth injury as well as postnatal metabolic transition. The abnormal body fat distribution at birth may destine some of these infants to lifelong obesity. Abnormal fetal growth in diabetic pregnancy appears to occur with any elevations in maternal glucose levels, however modest. Detection of macrosomia is therefore a major goal of diabetic pregnancy management.

Prediction of fetal macrosomia using sonographically measured abdominal subcutaneous tissue thickness

PURPOSE

We assessed the usefulness of sonographic measurement of abdominal subcutaneous tissue thickness in predicting fetal macrosomia (weight > 4,000 g).

METHODS

Abdominal subcutaneous tissue thickness was measured sonographically in 133 term fetuses. All studied fetuses were delivered within 72 hours after the measurements were taken.

RESULTS

One hundred thirteen fetuses were normal size, and 20 were macrosomic. The fetal abdominal subcutaneous tissue thickness ranged between 3 and 18 mm in all fetuses, with a mean measurement of 8.4 +/- 2.7 mm (standard deviation). The mean tissue thickness differed significantly between normal and macrosomic fetuses (7.0 mm versus 12.4 mm, respectively; p < 0.0001). There was a significant positive correlation between the abdominal subcutaneous tissue thickness and the birth weight (r = 0.67, p < 0.0001). The negative predictive value for a range of cut-off points between 8 and 13 mm varied between 84.3% and 100% (for prevalence rates of macrosomia of 5-25%). However, the positive predictive value was less than 50% for cut-off values below 11 mm.

CONCLUSIONS

Sonographic measurement of the subcutaneous tissue thickness of the fetal abdomen is useful for ruling out macrosomia.

Predicting birth weight by fetal upper-arm volume with use of three-dimensional ultrasonography

OBJECTIVE

Our purpose was to determine the usefulness and accuracy of the three-dimensional ultrasonography assessed fetal upper-arm volume in predicting birth weight.

STUDY DESIGN

From June 1996 to October 1996, we performed a prospective study of ultrasonography on 105 pregnant women without fetal structural anomaly or aneuploidy. Both the traditional two-dimensional ultrasonographic parameters and three-dimensional ultrasonography for fetal upper arm volume were measured within 48 hours of delivery.

RESULTS

The upper arm volume correlated well with birth weight (r = 0.92, n = 105, p < 0.0001). With use of linear and polynomial regression, we obtained a best-fit new formula, Birth weight = 1088.60 + 36.024 x Upper-arm volume. The accuracy of this new formula is compared with that of two Chinese equations predicting fetal weight reported before and other formulas commonly used in the world as well. Our formula is more accurate in predicting birth weight than all the other formulas by traditional two-dimensional ultrasonography, either in error, percentage error, or absolute error. Another group by prospective validation further proved this finding.

CONCLUSION

The upper-arm volume assessed by three-dimensional ultrasonography can accurately predict birth weight, and its accuracy is superior to the previous, formulas. Our study has at least validated the application of upper-arm volume by three-dimensional ultrasonography in estimating fetal weight. Further larger series are needed to confirm our findings.

The nurse's role in the identification of risks and treatment of shoulder dystocia

Shoulder dystocia is a clinical emergency that requires immediate recognition and prompt treatment to minimize maternal and neonatal sequelae. The nurse's role is to recognize and report associated risk factors for shoulder dystocia, respond with appropriate assistance, and monitor the woman and her newborn after delivery. The nurse's calm demeanor, knowledge of treatment modalities, and prepared response are valuable assets in this clinical dilemma.