The management of error in ultrasound fetal growth monitoring

It is important to understand the uncertainty in fetal measurements when using them in the management of pregnancy. The aim of this essay is to provide background on errors and uncertainty, describing error sources and their potential impact, with guidance on improving accuracy. Errors can be systematic or random, arising from equipment, image plane selection, measurement method and caliper placement and influenced by image quality, training and experience. The uncertainty in measurements is larger than clinically significant differences in fetal size and growth. Errors can be reduced by implementing equipment acceptance testing, written procedures, training and audit.     

The use of ultrasound in the assessment of normal fetal growth: A review

This review presents the basic principles underlying the quantitative assessment of normal fetal growth using ultrasound. Data on fetal growth derived from measurements of body, head, chest, and abdominal dimensions, are summarized, compared, and evaluated. Fetal volume and weight determination are also discussed. Most of the data evaluated were obtained in cross-sectional studies, but we present the preliminary results of our longitudinal study of fetal growth for comparison.     

新的腹围测量方法在超声胎儿体重估计中的应用价值

目的探索一种新的腹围测量方法在超声胎儿体重估计中的准确性,及临床应用价值。方法对226例孕妇采用相同的胎儿双顶径,头围,股骨测量方法,同时对同一胎儿用两种方法进行腹围测量,并分别估计胎儿体重,并与出生体重对比分析。结果两种腹围测量方法对不同分组胎儿体重的估计准确性无明显差异。并且两种腹围测值统计学分析亦无差异。结论实际工作中可根据情况选择更方便、更清晰、更易于显示的腹围层面进行测量,以便估计胎儿体重,新的腹围测量方法具有较好的临床应用价值。     

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.     

Use of the amniotic fluid index combined with estimated fetal weight within 10 days of delivery for prediction of macrosomia at birth.

OBJECTIVE: The purpose of this study was to assess the value of combining the sonographically estimated fetal weight (EFW) and amniotic fluid index (AFI) measured within 10 days of term delivery for prediction of macrosomia at birth. METHODS: Prospective sonographic fetal biometric measurements and delivery ward data of a single center, uploaded separately over a 4-year period, were retrospectively linked to yield an unselected sample of nondiabetic pregnancies with live-born term neonates. RESULTS: Of the 1925 pregnancies evaluated, 140 (7.2%) were macrosomic (birth weight > or =4000 g). The AFI was significantly higher in the macrosomic group (P < .001). On receiver operating characteristic curve analysis, the area under the curve was larger for predictions based on the EFW alone than on the AFI. An EFW of 4000 g or higher had a positive predictive value of 46.6% for macrosomia at birth. Use of the previously suggested combined EFW and AFI cutoffs of 3689 g and 119 mm, respectively, yielded a positive predictive value of 30.3%. CONCLUSIONS: Combined use of the EFW and AFI rather than the EFW alone does not improve prediction of macrosomia at birth.     

Estimated fetal weight in the detection of the small-for-menstrual-age fetus

The purpose of this study was to assess the value of calculated fetal weight in the detection of the small-for-menstrual-age fetus. An ultrasound screening scan was performed on 1624 singleton pregnancies at 30 weeks to 36 weeks, menstrual age. Head, abdomen, and femur diaphysis measurements were recorded and used to estimate fetal weight. These and other more widely used parameters were used to predict birth weight below the 10th percentile for menstrual age. Estimated fetal weight at 34 weeks achieved sensitivity of 100% and specificity of 70%, the best result for any parameter. Specificity is improved using growth measurements.     

Development of individual growth standards for estimated fetal weight: II. Weight prediction during the third trimester and at birth

Using a weight estimation procedure based of the Rossavik growth model, we have evaluated the possibility of establishing individual growth curve standards for fetal weight estimates and of predicting birth weights in the second trimester. In 20 normal fetuses delivered at term, 95% of the weight estimates obtained after 26 weeks' menstrual age (MA) were within +/- 22% of the predicted weight estimates. In these same fetuses the mean difference between birth weight estimates based on growth patterns before 26 weeks, MA, and actual birth weights was 1.2%, with 95% of the percent deviations being between 13.3% and - 8.8%. In a similar prospective study, the mean percent difference was -1.7%, with a range of 9.6% to -13.6%. Direct comparison of weight estimates obtained during the last week before delivery with birth weight projections indicated that birth weight estimates obtained 14 weeks before delivery had smaller systematic and random errors than those obtained within a week of delivery. These results indicate that individual growth curve standards for fetal weight estimates and the growth potential of individual fetuses can be determined from growth patterns in the second trimester.     

Evaluation methods for intrauterine growth using neonatal fat stores instead of birth weight as outcome measures: fetal and neonatal measurements correlated with neonatal skinfold thicknesses

Neonatal anthropometry, including timed skinfold measurements, was performed on 55 products of selected pregnancies. These skinfold measurements were compared with published standards of measurements obtained by similar techniques. Values outside the 3rd percentile to 97th percentile range were overlaid on the birth weight/menstrual age relationship of these subjects. Seven of 10 subjects with the lowest midtriceps skinfolds weighed more than 2500 g at birth (2 more than 3500 g) and 2 of 4 with the largest midtriceps skinfold had birth weights less than 4000 g. This comparison emphasizes the imprecision of birth weight as a measure of quality of fetal growth. Since skinfold thickness measurement is cumbersome for clinical use, other neonatal measures that may be more readily available to the clinician were examined for correlation with skinfolds. Simple birth weight/crown-heel length ratio was found to have the closest relationship of the parameters examined. Although estimated fetal weight was found to be the ultrasonography-derived parameter best correlated with skinfold thickness, ultrasonography discriminated poorly between babies with normal and low skinfolds. Low skinfold thickness predicted thermal vulnerability in the nursery better than did birth weight.     

低分子肝素治疗胎儿生长受限的效果及对围生儿结局的影响

目的 探索低分子肝素治疗胎儿生长受限的效果及对围生儿结局的影响.方法 选择120例胎儿生长受限的孕妇为试验对象,根据单双号随机化法将其分为对照组和观察组,各60例.对照组采用常规治疗,观察组采用低分子肝素治疗.比较两组的收缩期血液流速高值/舒张晚期血液流速高值(S/D)、阻力指数(RI)、搏动指数(PI)、胎儿每周生长...     

超声诊断胎儿肢体畸形的价值

目的探讨胎儿肢体畸形的二维超声图像特征。方法回顾性分析11例胎儿肢体畸形的二维超声检查结果和图像特征,并与产后及引产后的结果对照。结果超声明确诊断7例胎儿肢体畸形,漏诊4例。结论典型胎儿肢体畸形有二维图像特征,末端指趾易漏诊,因超声无创伤、安全,可反复检查,是诊断胎儿肢体畸形的首选方法。     

Ultrasonic fetal weight estimation: Analysis of inter- and intra-observer variability

Standard ultrasound measurements were performed by two observers in 40 third-trimester fetuses. Observers were blinded to the results of the meaurements. Estimated fetal weight (EFW) was calculated using two published formulae. The intra-observer standard deviation for EFW, assessed using one-way analysis of variance, was <75 g for both observers. The 95% prediction intervals for inter-observer comparisons of EFW, calculated using the limits of agreement method, were ? 187.3 g to 139.8 g, and ? 159.9 g to 124.3 g, using the two formulae. The results suggest that measurements of EFW are reproducible. The prediction interval is comparable to the weekly fetal weight increment in normal fetuses. © 1993 John Wiley & Sons, Inc.     

Association of amniotic fluid index with estimated fetal weight.

OBJECTIVE: The relationship between amniotic fluid volume and gestational age has been described previously. The association of body weight and urine output has been observed in human neonates. Our goal was to assess the correlation of the amniotic fluid index (AFI) with estimated fetal weight (EFW) in the third trimester. METHODS: We conducted a retrospective observational study on 426 pregnant women with singleton gestations who were referred to our unit for sonographic evaluation in the third trimester. The AFI, EFW, and EFW percentile corrected for gestational age were evaluated. The sonographic examinations were stratified into 3 gestational age categories: 28 through 33.9 weeks, 34 through 37.9 weeks, and 38 weeks and later. Maternal and fetal outcome variables were collected from medical records. Linear regression, Mann-Whitney U, and Kruskal-Wallis tests were used for statistical analysis. RESULTS: There was no significant relationship between the AFI and EFW in the entire group of patients (R = 0.08; P = .096). There was a significant relationship between the AFI and EFW after 38 weeks' gestation (R = 0.30; P = .003). In addition, in female fetuses the EFW percentile correlated with higher AFI values at all gestational ages (R = 0.31; P < .001); this, however, was not observed in male fetuses. CONCLUSIONS: There is no relationship between the AFI and EFW during the third trimester, although a positive relationship between the AFI and EFW was noted late in gestation. In pregnancies with female fetuses, the AFI was positively associated with EFW percentile before 38 weeks' gestation.     

Routine obstetric ultrasound: effectiveness of cross-sectional screening for fetal growth retardation

Sonographic detection of fetal growth retardation was evaluated on a sample of 778 patients routinely scanned over a 16-month period. From the 29th week to term, the sensitivity of abdominal circumference measurement progressively increased from 41% to 88% (P less than 0.01). Higher rates were achieved by using the biparietal diameter but false-positive diagnoses were twice as frequent as with the abdominal measurements. When the limitations in precision of abdominal circumference were considered, the screening rate of this parameter increased about 16%. Moreover, 50% of the false-negative diagnoses were made on fetuses weighing between the fifth and 10th centiles at birth. These diagnostic indices for biparietal diameter and abdominal circumference evaluated on a retrospective series proved to be lower than those reported for the prospective selected series. However, the results yielded by routine ultrasound were better than those obtained with clinical or traditional biochemical methods. These findings underline the importance of sonography not only in serial control of high-risk pregnancies but also in cross-sectional screening programs.     

A comparison of two different ultrasound methods for estimating fetal weight in preterm gestations

A prospective study was conducted to evaluate the estimation of fetal weight in preterm pregnancies by use of ultrasound measurements. Two equations for estimating fetal weight, one proposed by Shepard and associates and the other by Hadlock and associates, were evaluated. The ability to estimate fetal weight accurately was evaluated with respect to birth weight and menstrual age. Shepard's equation is associated with a lower mean signed percent error than Hadlock's, when the birth weight is less than 1500 g (4% vs 12%) or when the menstrual age is between 23 weeks to 30 weeks (2% vs 10%). However when the birth weight is between 1500 g and 3500 g, or the menstrual age is between 31 weeks to 36 weeks, Hadlock's equation has a lower mean signed percent error: 1% vs -4% for the birth weight category and 2% vs -3% for the menstrual age category. In preterm gestations both equations estimate fetal age weight with a low mean signed percent error--Shephard's -0.4% versus Hadlock's 6.0%.     

对比不同超声估重公式预测巨大胎儿体质量

目的 观察不同超声估重（SFEW）公式预测巨大胎儿的准确率，分析其影响因素。方法 回顾629例巨大儿，根据体质量分为A组和B组；将产前超声所测双顶径（BPD）、头围（HC）、腹围（AC）及股骨长（FL）代入不同公式，比较SFEW预测值与出生后实测值的差异。结果 不同估算公式SFEW测值均明显低于实测值（P均<0.001），其中Hadlock公式预测值与实测值的差异最小；产前超声生物学测值与出生后实测体质量及身长低度相关（r_s<0.50）。B组身长、体质量指数（BMI）及各超声生物学测值均明显大于A组（P均<0.05）；不同公式计算B组误差均明显大于A组（P均<0.05）。结论 SFEW有效可行，但易低估胎儿体质量，各公式参数不能充分体现巨大胎儿躯干外脂肪分布差异对体质量的影响可能是原因之一。     

正常双绒毛膜双胎孕期估重差异性及其影响因素

目的 探讨正常双绒毛膜双胎孕期超声估重（EFW）差异率及其影响因素。方法 回顾性分析550名正常双绒毛膜双胎（1 100胎）孕妇的产前孕期超声生物测量指标,并根据胎儿双顶径、头围、腹围、股骨长计算双胎EFW差异率,分析其与孕周的关系,观察性别、受孕方式（试管组与非试管组）是否影响EFW差异率。结果 正常双绒毛膜双胎EFW差异率总体呈偏态分布,中位数为6.56%,四分位间距为8.92%,第95百分位数为20.81%,与孕周无明显相关。性别相同组与性别不同组、不同受孕方式组间双胎EFW差异率差异均无统计学意义（P均>0.05）。结论 产前超声对双绒毛膜双胎估重有重要参考价值,EFW差异率可作为双绒毛膜双胎孕期生长评估相对恒定的指标。