Fetal Biometry Measurements Research Articles

Predictive value of a single early fetal weight estimate in normal pregnancies

Objectives To evaluate the accuracy of ultrasound-based fetal weight estimates made at 28–34 weeks of gestation in predicting small- and large-for-gestational-age infants (SGA, LGA) at term. Methods Two-hundred and fifty-nine patients with a healthy, singleton pregnancy in whom fetal biometry measurements were routinely performed between 28 and 34 weeks’ gestation, were recruited at term delivery. The sonographic estimated fetal weight (EFW) and the birth weight were converted to percentiles on the basis of locally developed growth charts and compared. Multivariate linear stepwise regression analysis was used to predict the birth weight and birth weight percentile. The resulting equation (projectile formula) was used to determine the calculated birth weight, and that value was compared with the actual birth weight. The Bland and Altman plot and Passing and Bablok regression were used to compare between the calculated birth weight and the actual birth weight. Results Mean gestational age at ultrasound examination was 32 ± 1.6 weeks (28–34), and mean age at delivery was 39 ± 1.7 weeks (37–42). The multivariate correlation between the calculated birth weight and the birth weight ( R 2 = 0.524) was higher than the correlation between the sonographic EFW and the birth weight ( R 2 = 0.083). Both the sonographic EFW and the calculated birth weight are characterized by low positive predictive values in predicting SGA or LGA infants. The calculated birth weight was more accurate in excluding SGA and LGA infants (negative predictive values of 99.5% and 100%, respectively). On method comparison tests, the calculated birth weight was not significantly different than the actual birth weight. Conclusions Fetal weight estimation at the early third trimester poorly predicts the birth weight centile at term. It remains uncertain, however, if it would be useful to use the calculated birth weight in pregnancies with clinically suspected SGA or LGA fetuses.

Ultrasound diagnosis of fetal macrosomia: a comparison of weight prediction models using computer simulation

To assess the frequency of the diagnosis of macrosomia in relation to differing weight estimation formulae in unselected pregnancies. Computer modeling techniques were employed. Computer modeling software generated correlated fetal biometry measurements according to published British standards, from 37 to 41 weeks' gestation. For each set of measurements, estimated fetal weights were obtained by a panel of 18 ultrasound weight formulae. The diagnosis of macrosomia was made if the fetal weight estimate was greater than 4500 g. Cohorts of 5000 pregnancies for each week of gestation were studied. The frequency of diagnosis of macrosomia increased progressively with advancing gestational age, with large increases between 40 and 41 weeks. The type of weight estimation formula had a profound influence on the frequency of diagnosis of macrosomia. Five of the formulae tested almost never returned a weight estimate greater than 4500 g. Three formulae yielded false positive rates in excess of 15%. The Hadlock group of formulae yielded frequencies of 0.3% to 14.6%. Most formulae tend to over-diagnose macrosomia at term. Intervention rates for suspected fetal macrosomia may be influenced by gestational age at the time of scan and the type of fetal weight estimation formula in use.

OC35.02: Individual and group learning curves for ultrasound fetal biometry measurements: cumulative sum analysis

OC35.02: Individual and group learning curves for ultrasound fetal biometry measurements: cumulative sum analysis

Third‐trimester ultrasound dating algorithms derived from pregnancies conceived with artificial reproductive techniques

To derive an accurate formula for ultrasound estimation of gestational age in late pregnancy. A database of 123 singleton pregnancies conceived by artificial reproductive techniques with third-trimester ultrasound measurements was studied. Biometry variables included the fetal head circumference (HC) and femur length (FL). The dataset was equally divided into a derivation sample and a target sample. To derive the equations of best fit, regression analysis was used, with true menstrual age as the dependent variable and fetal biometry measurements as independent variables. The formulae were tested on the target set and the menstrual age estimates were compared with the actual menstrual age. Clinical performance was estimated in terms of systematic and random errors, absolute errors and their 95% CI values. The menstrual ages at time of scanning ranged from 26 to 41 weeks, with a mean of 33 weeks. The best performing derived formula was a combination of HC and FL. This had a random error of 7.5 days and prediction errors within a 95% confidence limit of -13 to +17 days. With FL only, the random error was 8.2 days, whereas using the HC only yielded a random error of 9.4 days. Ultrasound estimation of gestational age in late pregnancy is better than indicated by older publications. It is more accurately estimated by combining the HC with the FL than by using the FL measurements alone.

Fetal growth in Peru: comparisons with international fetal size charts and implications for fetal growth assessment

To compare fetal biometry measurements obtained in a Peruvian population with reference fetal size charts obtained in Peruvian and non-Peruvian populations. Fetal biometry measurements collected prospectively in 195 uncomplicated pregnancies were included in the presented analysis. At 20, 24, 28, 32, 36 and 38 weeks' gestation, fetal head circumference, abdominal circumference and femur diaphysis length were measured. Fetal biometry measurements were compared with fetal size charts obtained from another Peruvian and two non-Peruvian populations from North America and Europe. When compared with ultrasound-based reference fetal size charts obtained from North American and European populations, fetuses from the studied population appeared to grow more slowly with advancing gestational age. This trend was not observed when a Peruvian population, similar to the one studied here, was used as a reference. The results suggest that fetal growth in this Peruvian population may not be adequately assessed by using reference charts obtained from other populations and have implications for the use of growth standards in antenatal management.

Isoprostanes in amniotic fluid: a predictive marker for fetal growth restriction in pregnancy

Isoprostanes are markers of free radical-catalyzed lipid peroxidation. Evidence suggests that oxidative stress occurs in pregnancies with fetal growth restriction (FGR). The aim of this study was to analyze F 2-isoprostanes in amniotic fluid of FGR pregnancies. We tested the hypothesis that F 2-isoprostanes are reliable markers to distinguish FGR pregnancies from normal ones and appropriate-for-gestational-age (AGA) from small-for-gestational-age (SGA) newborns. F 2-isoprostanes levels were measured by colorimetric enzyme immunoassay in the amniotic fluid of 77 pregnancies with normal fetal growth (group I) and 37 with FGR (group II). Fetal biometry and Doppler measurements were obtained using an ATL HDI 3000 ultrasound system. Isoprostanes were higher in group II than group I. The ROC curve distinguished group I from group II, showing 100% sensitivity and 88.3% specificity at a cutoff of 94 pg/ml. There were no statistical differences in isoprostanes levels between AGA and SGA newborns in group II. The area under the ROC curve drawn to distinguish AGA and SGA newborns showed a sensitivity of 100% and a specificity of 72.3% at a cutoff of 94 pg/ml. The relative risk index indicated a 8.05 times higher risk of birth weight below the 3rd percentiles in group II than in group I. High isoprostanes concentrations can be detected in the amniotic fluid of FGR pregnancies and the assay of isoprostanes in amniotic fluid is a reliable assessment of fetal oxidative stress. Common use of this predictive marker in obstetrics will improve the ability of clinicians to identify those fetuses who will be born SGA or with a birth weight below the 25th percentile.

P08.06: The effect of palm vitamin E supplementation on fetal growth and birth weight—a preliminary report

Objective: To investigate the effect of an antioxidant, palm vitamin E (Tri-E) on fetal growth and birth weight. Methods: This randomized double blind placebo-controlled clinical trial involved 113 primigravidae seen at the Antenatal Clinic of Hospital UKM. Supplementation of Tri-E (100 mg daily) was given from 12 to 16 weeks’ gestation onwards until delivery of the baby. Ultrasound measurement of fetal biometry was performed every four weeks from 20 weeks onwards. The head over abdominal circumference ratio (HA ratio) was calculated to indicate the fetal growth from 28 weeks’ gestation onwards. At delivery, birth weight was recorded. Statistical test using the independent samples t-test was performed for analysis. Results: Out of 113, 46 were in the study group and 67 were in the placebo group. There were no statistically significant differences in the HA ratio between the two groups at 32 weeks (mean 1.04 for study and mean 1.05 for placebo) and 36 weeks’ gestation (mean 1.00 for study; mean 1.01 for placebo) respectively. As for the birth weight, there were also no statistically significant differences between the study (mean birth weight: 2992 grams) and placebo group (mean birth weight: 3267 grams). Conclusion: Early supplementation with Tri-E starting from the first trimester did not result in acceleration of fetal growth and delivery of bigger babies at birth.

P14.67: Ultrasound estimation of fetal weight in prolonged pregnancy

Introduction: When performing fetal biometry measurements, the examiner occasionally has the impression that the sonographic estimation is less accurate due to technical limitations. Our objective was to evaluate the possible association between the examiners assessment of the measurement accuracy and the actual error between fetal weight estimation and actual birth weight. Methods: 186 women, within 10 days of delivery, were examined prospectively using fetal biometric measurements. Fetal weight estimates were calculated using Hadlock’s formula employing FL, AC and BPD. The sonographers were asked to give a subjective score to each measurement; one point if the quality of the measurement was technically good, two points if the measurement was of medium quality and three points if the measurement was of poor quality. The difference between the corrected sonographic fetal weight estimation and the actual birth weight was analyzed with respect to the scoring given by the examiner. Results: As shown in tables 1–3 for none of the three measured parameters did the perceived measurement accuracy predict the actual error in predicting birth weight.

P14.66: Can the sonographer predict the accuracy of sonographic estimation of birth weight?

Introduction: When performing fetal biometry measurements, the examiner occasionally has the impression that the sonographic estimation is less accurate due to technical limitations. Our objective was to evaluate the possible association between the examiners assessment of the measurement accuracy and the actual error between fetal weight estimation and actual birth weight. Methods: 186 women, within 10 days of delivery, were examined prospectively using fetal biometric measurements. Fetal weight estimates were calculated using Hadlock’s formula employing FL, AC and BPD. The sonographers were asked to give a subjective score to each measurement; one point if the quality of the measurement was technically good, two points if the measurement was of medium quality and three points if the measurement was of poor quality. The difference between the corrected sonographic fetal weight estimation and the actual birth weight was analyzed with respect to the scoring given by the examiner. Results: As shown in tables 1–3 for none of the three measured parameters did the perceived measurement accuracy predict the actual error in predicting birth weight.

The evaluation of cardiac biometry in major cardiac defects detected in early pregnancy.

The objective was to evaluate early cardiac biometry in fetuses with structural cardiac defects between 10 and 17 weeks of gestation using our normative data about fetal heart biometry. A retrospective case series, patients were selected from all cases with congenital heart disease diagnosed between 10 and 17 weeks of gestation in our prenatal unit between 1999 and 2000. A schematic sonographic examination, including nuchal translucency (NT) thickness measurements, was performed and was followed by fetal Doppler echocardiography. The transversal heart diameter, both ventricular dimensions, heart area, heart circumference, thoracic diameter, thoracic circumference, thoracic area, pulmonary trunk diameter and aortic diameter were measured and the cardiothoracic ratios were calculated. Doppler evaluation of the umbilical arteries, ductus venosus and umbilical vein was performed. Fetal karyotyping was obtained by amniocentesis or chorionic villous sampling. During the study period, 31 cases of congenital heart disease between 10 and 17 weeks of gestation were diagnosed. Of these, two fetuses presented with ectopia cordis and six with insufficient cardiac biometric measurements. In the remaining 23 fetuses, different complex abnormalities with a high rate of chromosomal abnormalities (91%) were present. Fetal heart biometry was normal in 22% and abnormal in 78%. NT thickness measurements were performed before 14 weeks of gestation and ten of 12 fetuses (83%) presented with an increased NT. Both fetuses with normal NT showed an abnormal fetal heart biometry. Venous Doppler evaluation was performed in 22 cases and 12 fetuses (55%) demonstrated an abnormal venous Doppler. There were ten fetuses (45%) with normal venous Doppler; in seven of these cases, fetal heart biometry was partly abnormal. This study shows the feasibility of first and early second trimesters' fetal echocardiography and the applicability of cardiac biometry in these instances. In this context, early fetal heart biometry and NT thickness measurements may be complementary methods for the prenatal diagnosis of some major congenital heart defects. In early pregnancy, some cardiac defects like tricuspid valve dysplasia, coarctation of the aorta, aortic stenosis, tetralogy of Fallot or pulmonary stenosis may already show similar changes in the relation of the diameters of the fetal heart and great arteries, as seen in the second trimester. Therefore, evaluating the different cardiac ratios may have a high diagnostic value in early pregnancy.

Determination of gestational age after the 24th week of gestation from fetal kidney length measurements.

To evaluate the application of kidney length measurement to the determination of gestational age between the 24th and 38th weeks and to compare its accuracy with that of other fetal biometric indices. Seventy-three women with singleton uncomplicated pregnancies underwent standard ultrasound fetal biometry and kidney length measurement every 2 weeks between 24 and 38 weeks' gestation. These measurements were used to date the pregnancies relative to crown-rump length dating between 8 and 10 weeks' gestation. Linear regression models for estimation of gestational age were derived from the biometric indices and kidney length. In addition, stepwise regression models were constructed to determine the best model for determining gestational age between 24 and 38 weeks. Comparisons were then made between the accuracy of these models in the determination of gestational age. The best model for estimating gestational age in late pregnancy included the variables kidney length, biparietal diameter, head circumference, femur length and abdominal circumference. This model accurately predicted gestational age with a standard error of +/- 8.48 days. A model including kidney length, biparietal diameter, head circumference and femur length accurately predicted gestational age with a standard error of +/- 8.57 days. These models were slightly more accurate than models derived from the biometric indices of biparietal diameter, head circumference and femur length (+/- 9.87 days), biparietal diameter, head circumference, femur length and abdominal circumference (+/- 9.45 days) and biparietal diameter and femur length (+/- 9.9 days). Kidney length and femur length were the most accurate single parameters for predicting gestational age using simple linear regression models (+/- 10.29 and 10.96 days, respectively); the abdominal circumference was the least accurate (+/- 14.54 days). Kidney length is a more accurate method of determining gestational age than the fetal biometric indices of biparietal diameter, head circumference, femur length and abdominal circumference between 24 and 38 weeks' gestation. When combined with biparietal diameter, head circumference and femur length, the precision of dating is improved by 2 days. This measurement is easy to make and could therefore be easily incorporated into the model for dating pregnancies after 24 weeks of gestation, in particular when measurements of the biparietal diameter and head circumference are difficult.

Fetal biometry at 4300 m compared to sea level in Peru.

The aim of this study was to compare ultrasound fetal size at high altitude and sea level. Three hundred and thirty-four women in Cerro de Pasco at 4300 m (14,100 ft) altitude and 278 women in Lima (sea level) were recruited to the study. Ultrasound fetal biometry was carried out between 14 and 42 weeks of gestation. Biparietal diameter, occipitofrontal diameter, abdominal circumference and femur length were measured and head circumference and estimated fetal weight were derived from these data. Two hundred and seventy-seven women (82.9%) in Cerro de Pasco and 216 (77.7%) in Lima had normal singleton pregnancies and certain menstrual dates. These women were selected for statistical analysis. Fractional polynomial regression analysis on gestational age was performed, controlling for maternal height and parity. Fetal biometry measurements were significantly smaller in Cerro de Pasco compared with Lima. When gestation bands were compared this effect was present from 25 to 29 weeks onwards, and was greater in the abdominal circumference than in the head circumference and femur length (ratios Cerro de Pasco: Lima, 0.96, 0.97 and 0.98, respectively). Estimated fetal weight was also significantly lower in Cerro de Pasco (ratio 0.88), as were birthweights (ratio 0.88). If the centiles derived from the Lima population were applied for Cerro de Pasco, 11.2% of all estimated fetal weights would be below the fifth centile, and 1.08% above the ninety-fifth. These data suggest that at high altitude, all fetal biometry measurements follow a lower trajectory than at sea level. Specific biometry charts should therefore be used for obstetric ultrasound at high altitude.

Ultrasonographic ear length measurement in normal second- and third-trimester fetuses

Objective: We sought to develop a nomogram for fetal ear length measurements from a large population of healthy second- and third-trimester fetuses and to investigate the correlation of fetal ear length with other standard fetal biometry measurements, as follows: biparietal diameter, head circumference, abdominal circumference, femur length, and humerus length. Study Design: Ear length measurement was obtained prospectively in 4240 singleton fetuses between 15 and 40 weeks’ gestational age. Either complete data for normal karyotype on amniocentesis or normal infant examination at birth or both were available in 2583 cases. These constituted the final study population. Results: A nomogram was developed by linearly regressing ear length on gestational age (Ear length [in millimeters] = 1.076 × Gestational age [in weeks] – 7.308). There was a high correlation between ear length and gestational age (r = 0.96; P =.0001). Conclusion: The results of this study provide normative data on growth of fetal ear length from 15 to 40 weeks’ gestation. Good correlation was also observed between ear length and other fetal biometric measurements (biparietal diameter, head circumference, abdominal circumference, femur length, and humerus length). (Am J Obstet Gynecol 2000;183:230-4.)

Endoscopic intrauterine fetal therapy: A monkey model

Objectives Prenatal ultrasonographic investigations have led to an increasing number of prenatally detected abnormalities, of which a large number involves the urogenital tract. This study was performed to evaluate if endoscopic intra-amniotic access is possible in primates. Methods In 10 midtrimester rhesus monkeys (Macaca mulatta), endoscopic intrauterine fetoscopy was performed with three access cannulas. Using a Seldinger technique, a vascular access system, and a Pediatric laparoscopy set, intra-amniotic inspection was attempted. Fetal growth throughout pregnancy was monitored by ultrasonographic measurements of fetal biometry. Results Intrauterine access could successfully be achieved in 10 rhesus monkeys with three cannulas. After partial amniotic fluid exchange, adequate fetoscopy was always possible. Two monkeys aborted on the second and sixth postoperative days. Serial ultrasonographic investigations for fetal biometry showed no disturbance of the intrauterine growth patterns in the remaining 8 monkeys. Conclusions We currently conclude that the rhesus monkey model for experimental intrauterine endoscopic surgery may be suitable for study of the developmental abnormalities of the genitourinary tract.

250 Ear Length in Second Trimester Aneuploid Fetuses

To test the hypothesis that small ears have diagnostic value in detecting second-trimester aneuploid fetuses by ultrasound.We prospectively studied 452 patients with singleton pregnancies undergoing ultrasound examination for genetic amniocentesis at 14-25 weeks and an additional 30 singleton pregnancies at 20-25 weeks with a negative anomaly screen. Standard fetal biometry measurements were obtained, including ear length (from helix to end of lobe).Of these patients, 424 (88%) had ear measurements obtained, and a nomogram for ear length by gestational age was compiled. The relationship between ear length and gestational age was linear across the second trimester (r = 0.84, P < .001). Fourteen fetuses had aneuploidy by amniocentesis, of whom ten had ear lengths at or below the tenth percentile. The sensitivity was 71% and the specificity 92% (377 of 410). Positive and negative predictive values were 23% (ten of 43) and 99% (377 of 381), respectively.Fetal ear length may be useful in identifying aneuploid fetuses sonographically during the second trimester.

Medical needs in the Gold Coast.

<h3>Introduction</h3> Up to 63% of cases of intra-partum hypoxia occur in pregnancies with no antenatal risk factors. Identification before labour of these antenatally normal fetuses at risk of intra-partum hypoxia would enable a more targeted approach to intra-partum care. <h3>Methods</h3> Five hundred and eleven women with uncomplicated, term, singleton pregnancies, underwent a pre-labour ultrasound assessment. This included measurement of fetal biometry, Umbilical artery, Middle cerebral artery, and Umbilical venous resistance indices. Clinicians managing the labour were blinded to the ultrasound results. Following delivery, case notes were reviewed and intra-partum outcomes correlated with ultrasound findings. <h3>Results</h3> Infants born by Caesarean section for presumed fetal compromise had the highest Umbilical artery pulsatility index (p = 0.002), the lowest Middle cerebral artery pulsatility index (p &lt; 0.001), the lowest cerebro-umbilical ratio (p &lt; 0.001), the lowest Umbilical venous flow rates (p = 0.003), and the highest cerebral blood flow of any mode of delivery group (p = 0.007). A cerebro-umbilical ratio &lt;10th centile has a positive predictive value of 36% for Caesarean section for presumed fetal compromise. This can be improved to 61.5% by inclusion of the other Doppler parameters. A cerebro-umbilical ratio &gt;90th centile has a 100% negative predictive value. <h3>Conclusion</h3> Pre labour fetal Doppler assessment can identify fetuses at both high and low risk of subsequent compromise in labour. Current intra-partum monitoring has a high false positive rate, which could be improved by better risk stratification prior to labour. This technique is easily translatable into clinical practise and would allow risk stratification of normal pregnancies prior to labour, enabling a more targeted approach to intra-partum care.