Transvaginal fetal biometry in early pregnancy

Typical changes of ethmocephaly and holoprosencephaly in a fetus at 14 weeks of gestation

Background

This case report is to show the details of the face of a very rare ethmocephaly at 14 weeks of gestation.

Case presentation

After the regular transabdominal two-dimensional (2D) scan for nuchal translucency we could describe the following malformations: holoprosencephaly, proboscis and an abnormal face, omphalocele containing bowel, hyperechoic kidneys and megacystis. In addition, we acquired transvaginal three-dimensional (3D) ultrasound volume blocks of the fetal head, scanned with different insonation angles and stored them for later analysis. Using the multiplanar mode the volume blocks taken from the front show all details of the face: proboscis, hypotelorism, microphthalmia, cleft palate, accelerated development of the frontal bones and premature closure of the metopic suture. The volume blocks taken through the squamosal suture show all details of the fossa posterior and brain: fused thalami surrounded by the typical monoventricle, normal brain stem, elongation of anterior membranous area. Render mode shows a precise 3D image of the face. To better demonstrate the changes of the fetal face a post-mortem photo of the fetal face is included.

Conclusion

This case report can demonstarte the typical changes of ethmocephaly in the first trimester using transvaginal 3D scan.

Morphogenesis of the femur at different stages of normal human development

The present study aimed to better characterize the morphogenesis of the femur from the embryonic to the early fetal periods. Sixty-two human fetal specimens (crown–rump length [CRL] range: 11.4–185 mm) from the Kyoto Collection were used for this study. The morphogenesis and internal differentiation process of the femur were analyzed in 3D using phase-contrast X-ray computed tomography and magnetic resonance imaging. The cartilaginous femur was first observed at Carnegie stage 18. Major anatomical landmarks were formed prior to the initiation of ossification at the center of the diaphysis (CRL, 40 mm), as described by Bardeen. The region with very high signal intensity (phase 5 according to Streeter’s classification; i.e., area described as cartilage disintegration) emerged at the center of the diaphysis, which split the region with slightly low signal intensity (phase 4; i.e., cartilage cells of maximum size) in fetuses with a CRL of 40.0 mm. The phase 4 and phase 5 regions became confined to the metaphysis, which might become the epiphyseal cartilage plate. Femur length and ossified shaft length (OSL) showed a strong positive correlation with CRL. The OSL-to-femur length ratio rapidly increased in fetuses with CRL between 40 and 75 mm, which became moderately increased in fetuses with a CRL of ≥75 mm. Cartilage canal invasion occurred earlier at the proximal epiphysis (CRL, 62 mm) than at the distal epiphysis (CRL, 75 mm). Morphometry and Procrustes analysis indicated that changes in the femur shape after ossification were limited, which were mainly detected at the time of initial ossification and shortly after that. In contrast, femoral neck anteversion and torsion of the femoral head continuously changed during the fetal period. Our data could aid in understanding the morphogenesis of the femur and in differentiating normal and abnormal development during the early fetal period.

Fetal biometry: Relevance in obstetrical practice

Ultrasound imaging in obstetrics and gynecology dates back to 1958 when The Lancet published the first article about the use of ultrasonography for fetal and gynecological assessments. It is now almost inconceivable, 60 years later, to think of effective performance in obstetrics and gynecology without the variety of ultrasound, for example, real time imaging, power and color Doppler, 3D/4D ultrasonography, etc. Such examinations facilitate the assessment of intrauterine fetal growth and development during pregnancy, provide alerts about the risk of pre-eclampsia and preterm birth, help identify anatomic reasons for infertility, diagnose ectopic pregnancies, uterine, ovary and tubal pathology. Ultrasonography is also used for diagnostic and treatment procedures during pregnancy or for the treatment of infertility. This article is an overview of the development of fetal ultrasound, the methodology and interpretation of ultrasound in the assessment of intrauterine fetal growth and fetal biometry standards both worldwide and in Lithuania.

PRENATAL DIAGNOSIS OF SKELETAL DYSPLASIAS

Skeletal anomalies occur with a frequency of around 1:500 and can present a diagnostic challenge when detected prenatally. Increasingly more sophisticated imaging such as MRI or CT may elucidate features more easily interpreted by postnatal radiologists. The aetiology of these anomalies is varied and includes aneuploidy, genetic syndromes, skeletal dysplasias, teratogens, disruption and maternal disease, making a multidisciplinary approach to the diagnosis essential. The estimated prevalence of skeletal dysplasias varies from 2–3/10,000 to 4–7/10,000 and diagnosis may require biochemical, cytogenetic, molecular genetic or haematological investigation. Clinical genetic input is often required as the family history or parental examination may yield valuable clues to the diagnosis. This review will briefly describe the normal embryology and sonographic appearances of fetal limb development and go on to suggest a systematic approach to the diagnosis of fetal skeletal dysplasias.

First-trimester fetal limb biometry in Chinese population

OBJECTIVES

To establish reference ranges for fetal limb biometry obtained by transabdominal ultrasound examination at 12-14 weeks of gestation in Chinese women.

METHODS

A total of 1489 normal singleton fetuses between 12(+0) and 14(+6) weeks of gestation were examined transabdominally by two experienced observers. The gestation was ascertained by measurement of fetal crown-rump length (CRL) or biparietal diameter (BPD) and head circumference (HC). The lengths of the humerus and femur were prospectively worked out.

RESULTS

Gestation-specific reference ranges for limb measurements were calculated. The femur length (FL) (mean +/- SD) was 9.15 +/- 1.44 mm at 12-12(+6) weeks, 11.45 +/- 1.35 mm at 13-13(+6) weeks, and 13.64 +/- 1.60 mm at 14-14(+6) weeks; the corresponding humerus length (HL) (mean +/- SD) was 9.63 +/- 1.44 mm, 12.01 +/- 1.41 mm, 14.29 +/- 1.48 mm, respectively.

CONCLUSIONS

There was a general increase in fetal limb biometry with gestation. Fetal limb length can be an early marker of early growth restriction as well as fetal skeletal dysplasia among women in the local population.

Cardiac Circumference Measurement: Possible Screening Tool in Early Pregnancy for Anomalous Cardiac Development

OBJECTIVE

In this study, cardiac circumference (CC), measured by transvaginal sonography, was analyzed to determine the growth during the early stage of pregnancy and its relationship to abdominal circumference and femur length (FL).

METHODS

Biometric measurements, including CC, were obtained in 1,182 euploid fetuses at 9-16 weeks' gestation. The CC measurements were related to gestational age (GA), abdominal circumference, and FL. The corresponding 95% confidence intervals were calculated.

RESULTS

A linear growth function was observed between CC (mm) and GA (days) (r2 = 0.601; p < 0.0001; y = 0.573 GA - 24.185). Similarly, a good correlation is described with a linear function between CC (mm) and abdominal circumference (mm) (r2 = 0.70; p < 0.0001; y = 0.343 AC + 3.696) and between CC (mm) and FL (mm) (r2 = 0.626; p < 0.0001; y = 1.335 FL + 14.444). The regression analysis that best correlates the dependent variable CC (mm) with the independent variables, GA (days), abdominal circumference (mm), and FL (mm), is: y = 0.137 GA + 0.235 AC + 0.199 FL - 3.303 (r2 = 0.708; p < 0.0001).

CONCLUSION

Our results provide normative data of the growth of the CC in early pregnancy. The good correlation described between CC and abdominal circumference and FL suggests that cardiac measurements in early pregnancy alone, or related to other fetal biometric parameters, could be used as a screening tool to identify fetuses at risk for abnormal heart development.

Ultrasound dating at 12-14 or 15-20 weeks of gestation? A prospective cross-validation of established dating formulae in a population of in-vitro fertilized pregnancies randomized to early or late dating scan

OBJECTIVES

To determine the accuracy of established ultrasound dating formulae when used at 12-14 and 15-20 gestational weeks.

METHODS

A total of 363 singleton pregnancies conceived after in-vitro fertilization (IVF) and randomized to a dating scan at 12-14 or 15-20 gestational weeks were studied. 'True' gestational age was calculated on the basis of the day of oocyte retrieval and was compared to gestational age calculated on the basis of seven dating formulae including the fetal biparietal diameter (BPD) and three dating formulae including BPD and fetal femur length (FL). The mean of the differences between estimated and true gestational age (systematic measurement error) and their SD (random measurement error) were calculated for each formula.

RESULTS

Three formulae showed systematic errors of less than -0.7 days at both early and late scanning. Two formulae overestimated gestational age at both early and late scanning by 5.7 and 3.1 vs. 2.3 and 2.8 days, respectively, while five formulae manifested very different systematic errors at early and late scanning. The formulae used for clinical management underestimated gestational age by a mean of 3 days when dating was performed at 12-14 weeks, and by a mean of 0.8 days when dating was done at 15-20 weeks. The random error was on average 1 day less when the scan was carried out early (2 vs. 3 days; P < 0.0005). Mean true gestational age at delivery in IVF pregnancies with spontaneous start of labor was 279 days (SD 12.9); excluding preterm deliveries it was 281 days (SD 8.1).

CONCLUSIONS

Ultrasound dating formulae originally intended for use in the middle of the second trimester do not necessarily perform well when used for dating earlier in gestation. The systematic and random error of any dating formula must be assessed for the gestational age interval in which the formula is intended to be used.

Intra- and interobserver repeatability of femur length measurement in early pregnancy

OBJECTIVE

To assess the intra- and interobserver reproducibility of songographic measurement of fetal femur length between 10 and 16 weeks of gestation.

METHODS

Femur length was measured three times by the same trained observer in each fetus of 136 pregnant women. A second trained observer then repeated the measurements. The coefficient of variation, intraclass correlation coefficient and repeatability coefficient with 95% CIs were calculated for each observer and between the two observers.

RESULTS

The inter- and intraobserver repeatabilities of femur length were good. For interobserver correlation, the coefficient of variation was 4.6% (95% CI, 3.0-6.2), the intraclass correlation coefficient was 0.82 (95% CI, 0.69-0.95) and the repeatability coefficient was 2.1 (95% CI, 1.8-2.7). For intraobserver correlation, the coefficient of variation was 4.2% (95% CI, 3.2-5.6), the intraclass correlation coefficient was 0.91 (95% CI, 0.75-0.97) and the repeatability coefficient was 3.23 (95% CI, 2.33-3.86) for Observer 2. Similar results were obtained for the other observer.

CONCLUSION

Transvaginal femur length measurement is technically feasible and easy to perform between 10 and 16 weeks of gestation. The high degree of intra- and interobserver repeatability indicates it to be a reproducible method.

Femur and humerus length in trisomy 21 fetuses at 11-14 weeks of gestation

OBJECTIVE

To determine the value of measuring fetal femur and humerus length at 11-14 weeks of gestation in screening for chromosomal defects.

METHODS

Femur and humerus lengths were measured using transabdominal ultrasound in 1018 fetuses immediately before chorionic villus sampling for karyotyping at 11-14 weeks of gestation. In the group of chromosomally normal fetuses, regression analysis was used to determine the association between long bone length and crown-rump length (CRL). Femur and humerus lengths in fetuses with trisomy 21 were compared with those of normal fetuses.

RESULTS

The median gestation was 12 (range, 11-14) weeks. The karyotype was normal in 920 fetuses and abnormal in 98, including 65 cases of trisomy 21. In the chromosomally normal group the fetal femur and humerus lengths increased significantly with CRL (femur length = - 6.330 + 0.215 x CRL in mm, r = 0.874, P < 0.0001; humerus length = - 6.240 + 0.220 x CRL in mm, r = 0.871, P < 0.0001). In the Bland-Altman plot the mean difference between paired measurements of femur length was 0.21 mm (95% limits of agreement - 0.52 to 0.48 mm) and of humerus length was 0.23 mm (95% limits of agreement - 0.57 to 0.55 mm). In the trisomy 21 fetuses the median femur and humerus lengths were significantly below the appropriate normal mean for CRL by 0.4 and 0.3 mm, respectively (P = 0.002), but they were below the respective 5th centile of the normal range in only six (9.2%) and three (4.6%) of the cases, respectively.

CONCLUSION

At 11-14 weeks of gestation the femur and humerus lengths in trisomy 21 fetuses are significantly reduced but the degree of deviation from normal is too small for these measurements to be useful in screening for trisomy 21.

Early transvaginal fetal orbital measurements: a screening tool for aneuploidy?

OBJECTIVE

To assess whether simple biometric parameters such as orbital diameters measured in early pregnancy by transvaginal sonography can be used as screening tools for aneuploid fetuses.

METHODS

The study group consisted of 2771 fetuses of pregnant women referred to our center for genetic amniocentesis and examined by transvaginal sonography between 11 and 16 weeks' gestation. Karyotypes were normal in 2717 fetuses, and 54 fetuses were aneuploid. Individual values for the aneuploid fetuses were compared with normative data obtained previously for single orbital measurements (interocular and binocular distance) versus gestational age and head measurements.

RESULTS

The orbital diameters were within the normal range in the cases with trisomy 21, gonosomal aberrations, trisomy 18, and unbalanced anomalies. Three of the 4 fetuses with trisomy 13 had hypotelorism, confirmed later at autopsy in 2 cases and after delivery in 1 case.

CONCLUSIONS

With regard to the small number of cases, our data suggest that ocular biometric parameters may be useful sonographic markers for trisomy 13, even if further evaluation is needed.

Evaluation of femur/foot and humerus/foot ratios by transvaginal sonography between 62 and 116 days of gestation

OBJECTIVE

The objective was to construct nomograms of femur/foot length and humerus/foot length ratios in early pregnancy by transvaginal sonography.

METHODS

In the period 1994-2000, 1,008 singleton pregnant patients were examined from 62 to 116 days of gestation using transvaginal high-resolution ultrasound technique. As a part of biometric survey femur, humerus and foot length were recorded and evaluated as ratio at each gestational age. The distribution of the residuals for the different ratios is also described.

RESULTS

A significant correlation was demonstrated between femur and foot length (R2=0.984; p<0.0001) and between humerus and foot length (R2=0.983; p<0.0001). The femur/foot length and humerus foot/length ratios were approximately 1 throughout this period of gestation with a narrow range.

CONCLUSION

The presented data obtained in early pregnancy by transvaginal scan offer normative measurements of femur/foot length and humerus foot/length ratios which may be useful in the prenatal diagnosis of congenital syndromes that include skeletal maldevelopment.

Reference values for fetal limb biometry at 10-14 weeks of gestation

OBJECTIVES

To calculate reference ranges for fetal limb measurements obtained by transabdominal ultrasound at 10-14 weeks of gestation.

METHODS

Six hundred and six normal fetuses were examined transabdominally in a cross-sectional study by a single observer. The crown-rump length of the fetuses ranged from 31 to 78 mm. Measurement of the length of the humerus, ulna, femur, tibia and foot was attempted from the longest section of each structure. To assess intraobserver repeatability, three sets of repeated measurements were obtained in 26 fetuses.

RESULTS

An appropriate ultrasound measurement was obtained in a percentage of cases ranging from 93.2% to 97.9%. A significant correlation was found between crown-rump length measurements and humerus length (r = 0.74, P < 0.001), ulna length (r = 0.70, P < 0.001), femur length (r = 0.77, P < 0.001), tibia length (r = 0.69, P < 0.001) and foot length (r = 0.58, P < 0.001). Crown-rump length-specific reference ranges for each measurement were calculated with the method of scaled absolute residuals. The study of intraobserver variability showed coefficients of variation ranging from 7.9 to 10.0% and intraclass correlation coefficients ranging from 0.89 to 0.94.

CONCLUSIONS

Fetal limb size is strongly correlated with crown-rump length. Despite a significant biological variability of the measurements, the availability of reference ranges could be of help in the early diagnosis of fetal skeletal dysplasias.

Ultrasound diagnosis of structural abnormalities in the first trimester

The advances in ultrasound technology have made it possible to identify fetal structural abnormalities and genetic syndromes in the first trimester. First trimester prenatal diagnosis of fetal central nervous system, renal, gastrointestinal, cardiac, and skeletal abnormalities is reviewed.

A new mathematical formula for predicting long bone length in early pregnancy

OBJECTIVE

To propose new mathematical formulae to estimate fetal long bone biometry in early pregnancy and to establish their efficacy in comparison to previously constructed mathematical formulae.

METHODS

A study population of 1960 singleton euploid fetuses was referred for transvaginal ultrasound examinations between 71 and 112 days of gestation prior to genetic amniocentesis. To determine the relationship between the biparietal diameter and long bone length, a sample group of 400 randomly chosen normal fetuses was evaluated. Regression equations were derived, then tested in the remaining 1560 control fetuses and compared with previously reported mathematical formulae by other authors. Mean absolute error, mean absolute percentage error and mean systematic error with their standard deviations were calculated.

RESULTS

The relationships between femur or humerus length vs. biparietal diameter (BPD) and gestational age (GA) were, respectively: expected femur length = -16.92108 + 0.4569402 x BPD + 0.171617 x GA (P < 0.001) and expected humerus length = -16.28531 + 0.4283019 x BPD + 0.1696017 x GA (P < 0.001). The confidence intervals of the predicted values for different values of biparietal diameter and gestational age and confidence intervals for the regression coefficients, such as the distribution of the residuals, are given. All previous formulae obtained by transabdominal ultrasound demonstrated an overestimation of expected long bones measurements; this was reduced using different formulae obtained in early pregnancy. Using our mathematical formulae, the mean absolute percentage error and the mean systematic error in estimating femur and humerus length were very low (11.15% and -2.02%; 10.59% and -1.74%, respectively).

CONCLUSIONS

The new ultrasonographic morphometric models derived from transvaginal measurements in early pregnancy show a good reliability in estimating fetal long bone length.

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.