Ultrasound examination and measurement of fetal biometry has become an integral part of modern obstetric care. These measurements can serve for dating pregnancies or for assessment of fetal growth. However, to ensure accurate diagnosis, selection of the appropriate cross-sectional reference charts is of considerable importance.
Fetal biometry is an important part of routine examinations during the second and third trimesters of pregnancy. The use of cross-sectional reference charts and equations from a population as similar as possible to the screened population remains the gold standard. It has been demonstrated that the choice of reference charts and equations for fetal size has a significant impact on the quality of fetal biometry.
One of the main objectives of antenatal care is early diagnosis and appropriate management of pregnancies complicated with intrauterine fetal growth retardation (IUGR). In Egypt, as in many other developing countries, ultrasound measurements of fetal size are invariably compared with cross-sectional-derived reference ranges obtained from pregnancies of Anglo-Saxon or American populations. This practice is still adopted despite the fact that several studies have demonstrated significant ethnic variations in the fetal size and growth (Kurmanavicius et al., 1999; Jacquemyn et al., 2000). There has been a growing interest in adjusting fetal size charts for genetic influence; this has resulted in a renewed body of publications regarding race-adjusted and/or customized fetal size charts. It is well known that ethnicity has a significant influence on fetal biometry (Yeo et al., 1994; Jacquemyn et al., 2000).
The objectives of the present study are to develop pilot ultrasound fetal biometry data for Egyptian fetuses between 14 and 24 weeks of gestation and to deal with the concern of the need to develop local reference charts.
Patients and methods
The sample consisted of 71 women with singleton pregnancy; the gestational ages (GA) ranged from 14 to 24 completed weeks. They were referred to the outpatient clinic of the Prenatal Diagnosis and Fetal Medicine Department at the National Research Centre. Their age ranged between 18 and 35 years at the expected date of delivery. The GA was established by reference to the first day of the last menstrual period in patients with a history of regular menses, a close relation (±1 week) between the menstrual age and the ultrasound evaluation. Exclusion criteria included an uncertain date of the last menstrual period, irregular menstrual cycles, maternal disease possibly affecting fetal growth, such as hypertension, diabetes mellitus, renal disease, multiple pregnancies, and fetal malformations. Patients who fulfilled the inclusion criteria and who gave informed consent to participate in the study were assigned an appointment at which fetal biometric measurements were performed. All fetal biometric measurements were obtained by one sonographer. Cases were evaluated by the Voluson 730 system (GE Healthcare, Milwaukee, Wisconsin, USA) with a 3.5 MHz convex probe for two-dimensional ultrasound examinations.
Two-dimensional sonography was carried out to measure biparietal diameters (BPD), head circumferences (HC), abdominal circumferences (AC), and femur lengths (FL). Three measurements for each parameter were used to calculate the mean. Fetal head measurements were made in an axial plane at the level where the continuous midline echo is broken by the cavum septi pellucidi in the anterior third and that includes the thalamus. This transverse section should demonstrate an oval and symmetrical shape. Measurement of the BPD was from the outer edge of the closest temporomandibular bone to the inner edge of the opposite temporomandibular bone (Altman and Chitty, 1997). The HC was measured around the calvarium from the same axial image as for the BPD. The electronic ellipse method was used. For AC, a section that was as close as possible to circular, identifying the spine posteriorly, the umbilical vein in the anterior third and the stomach bubble in the same plane, was obtained. AC was also measured by the ellipse method. The ellipse was set at the outer margins of the soft tissues. FL was a straight measurement from one end of the femoral diaphysis to the other end, disregarding any curvature of the femur; the femoral head and the distal femoral epiphysis were not included. The transducer was rotated until the full femoral diaphysis was seen in a straight angle to the ultrasound beam (Chitty et al., 1994).
Statistical analysis was performed using the Statistical Package for Social Sciences, version 13.0 (SPSS Inc., Chicago, Illinois, USA).
Table 1 shows the mean of BPD, HC, AC, and FL according to GA in completed weeks in Egyptian singleton pregnancies. BPD shows an increase with GA; the maximum increase in the present measures is between the 23rd and the 24th weeks; this increase was equal to 4.83 mm, whereas the least increase is between the 21st and the 22nd weeks, and this increase was equal to 2.20 mm. HC shows an increase with GA; the maximum increase is between the 22nd and the 23rd weeks; this increase was equal to 17.5 mm, whereas the least increase is between the 21st and the 22nd weeks, and this increase was equal to 5.2083 mm. FL shows an increase with GA; the maximum increase is between the 14th and the 15th weeks; this increase was equal to 4.33 mm, whereas the least increase is between the 16th and the 17th weeks, and this increase was equal to 2.04 mm. The AC shows an increase with GA; the maximum increase is between the 15th and the 16th weeks; this increase was equal to 24.5 mm, whereas the least increase is between the 17th and the 18th weeks, and this increase was equal to 3.67 mm.
Figure 1 shows the comparison of our fetal biometry with the Italian population (Paladini et al., 2005). Figure 2 shows the comparison of the present data with the UK population (Altman and Chitty, 1997) at the median. Differences were observed between our fetal biometric results and those of the Italian and the UK populations, which were more pronounced in the FL measurements. However, our data are closer to the Italian data, especially for HC.
Fetuses that fall below the normal percentiles for the given GAs have a risk of developing IUGR, and hence, defining appropriate normal percentile ranges is important. Racial variation in ultrasound fetal biometry measurements has been demonstrated previously. In this respect, several authors have emphasized the value of using customized fetal growth charts that take care of variables such as maternal weight, parity, race, etc. (Gardosi, 1994; Pang et al., 2003). There has been a growing interest in adjusting fetal size charts for genetic influence: this has resulted in a renewed body of publications regarding race-adjusted and/or customized fetal size charts (Bernstein et al., 1996; Jacquemyn et al., 2000; Chung et al., 2003). Papaioannou et al. (2010) constructed normal ranges for embryonic crown-rump length (CRL), heart rate (HR), gestational sac diameter (GSD), and yolk sac diameter (YSD) at 6–10 weeks of gestation. The study reported significant quadratic associations between CRL, GSD, YSD, and gestation, and between HR, GSD, YSD, and CRL, and a cubic association between HR and gestation.
In the present study, fetal biometry of the local population was compared with some of the widely used populations and an Arabian population. We compared our pilot biometric measurements with those published from British (Altman and Chitty, 1997; Loughna et al., 2009), French (Salomon et al., 2006), Italian (Paladini et al., 2005), and Saudi Arabian (Nasrat and Bondagji, 2005) populations. A comparison of our data with those of UK (Altman and Chitty, 1997) and Italian (Paladini et al., 2005) data was carried out. The results of analysis of variance (Kruskal–Wallis test) between the measurements of the BPD, HC, AC, and FL of the present study and other western studies at the median and the 5th and 95th percentiles were statistically significant (P<0.0001) at all points of GAs, indicating that data are obtained from statistically different populations.
Marked variations between different populations in fetal measurements were observed, particularly at the extremes of ranges of fetal measurements, 5th and/or 95th percentiles. The consistency of such variations between different studies cannot be attributed to technical variables alone. Racial variation in newborn birth weight is well recognized and bound to be associated with similar variations in intrauterine fetal morphometric measurements. A comparison of our pilot data with those of Italian and UK populations at the 50th centiles are shown in Figs 1 and 2, respectively, for HC and FL. A marked difference was observed in the FL measurements as compared with both Italian and British populations. However, our data were closer to the Italian data, especially for HC. In addition, we compared our data with those of Johnsen et al. (2006) in Norway, which included 650 low-risk pregnancies, with the GA ranging from 10 to 40 weeks. A comparison showed BPD values lower than those of Johnsen et al. (2006) between the 20th and the 23rd weeks, higher values for HC from the beginning of the 14th week, which decreased gradually with progression of GA till the 22nd week, higher values for AC from the beginning of the 14th week and a gradual decrease with progression of GA till the 19th week, and higher FL values from the beginning of the 14th week till the 24th week at a constant difference of 1 week. These differences may be attributed to the difference in methodology, racial variation, or both; moreover, pregnancies with maternal or fetal complications were not withdrawn in the study of Johnsen et al. (2006).
The variation in fetal FL with respect to maternal race using fetuses of 39 Asian mothers, 31 black mothers, and 100 white mothers was reported previously. The fetal FL varies according to race; African American fetuses had longer-than expected FLs, and Asian fetuses had shorter-than-expected FLs compared with white fetuses (Shipp et al., 2001). The impact of race and ethnicity on the expected HL by BPD measurement in second-trimester fetuses was studied by Zelop et al. (2003). Ultrasound, obstetric, and cytogenetic databases from 1995 through 2001 for all normal fetuses between 15 and 22 weeks’ gestation were studied. The 11 278 fetuses including 4202 African American, 2269 Hispanic, 639 Asian, and 4168 white fetuses. The study concluded that race and ethnicity do not appear to affect the mean regression line of the expected HL by BPD among fetuses in the second trimester. In contrast, in a study conducted in Belgium (Jacquemyn et al., 2000) on 524 fetuses, 369 (70.4%) Belgian, 77 (14.7%) Moroccan, and 78 (14.9%) Turkish, it was found that fetuses of Turkish and Moroccan women had a shorter FL, AC, and HC than those of Belgian women. In a previous longitudinal study on fetal growth in Saudi Arabia, it was shown that there was a significant change in the rate of growth of fetal BPD from a mean increment rate of about 8% per week at 18 weeks to 3.9 and 1.3% increments per week at 28 and 38 weeks, respectively (Nasrat, 1997). FL measurements have the same utilization as for head measurements in the first half of gestation. Therefore, it might be important to pay more attention to ethnic variation in the fetal FL. In the third trimester, FL measurements are often included, together with AC measurements, in the equation for the estimation of the GA.
Racial variation in newborn birth weight is well recognized and bound to be associated with similar variations in intrauterine fetal morphometric measurements. In practice, it seems that variations in fetal biometry are an inevitable finding. The important point, however, pertains to the clinical significance of such variations. A short femur has been reported as one of the soft markers associated with Down syndrome. Hence, it might be important to pay more attention to ethnic variation in the fetal FL. Furthermore, the study emphasizes the importance of using specific population-based parameters for other disorders such as skeletal dysphasias. In the third trimester, FL measurements are often included, together with AC measurements, in the equation for the estimation of GA. Therefore, using cut-off points, for example, 10th or 5th percentile, based on AC charts driven from different populations would potentially increase the risk of either overdiagnosis or underdiagnosis of IUGR fetuses and vice versa. The consistency of such variations between different studies cannot be attributed to technical variables alone.
In conclusion, we have constructed a new set of pilot data for fetal biometric measurements for Egyptian singleton pregnancies. Our data were not similar to those of other populations. The main difference between our fetal biometric results and those of the UK and the French populations was in the FL measurements. The study emphasizes that genetic, environmental, and intergenerational effects are important factors that may play significant roles in the racial difference of fetal biometry. Therefore, the study recommends the development of national fetal biometric charts that can be used for the assessment of fetal growth and in clinical practice.
Conflicts of interest
There are no conflicts of interest.
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