The binocular distance: a new way to estimate fetal age

Fetal facial bone growth: Post-mortem CT analysis

OBJECTIVE

To describe and model the normal growth of fetal facial bones and angles.

MATERIAL AND METHODS

A total of 118 fetal CT scans obtained at 19 to 41 weeks gestation after in utero fetal death or late miscarriage were analyzed. CT scan was followed by autopsy and pathological examination and only fetuses free from brain disease or abnormal craniofacial development were included. The measurements were taken using software for frontal, sagittal and 3D reconstruction from native axial sections. The optimal plane for bone analysis was chosen and the measurements made by multiplanar reconstruction.

RESULTS

There was a statistically significant increase (P<0.001) in all measurements regardless of gestational age (GA) except those of the mandibulo-fronto-maxillary angle (P=0.412), the naso-mandibulo-maxillary angle (P=0.828) and mandibular width (P=0.86). There was no significant difference according to fetal sex. Based on these results, the corresponding growth curves were created. The anteroposterior mandibular diameter (APD) was very strongly correlated with GA (R=0.926, P<0.001). The following equation: GA=(8.187×APD)+4.257 can be used to estimate GA with a confidence interval (CI) of±2.42. The same applies to maxillary width (MW) (R=0.922; P<0.001). The equation GA=(11.059×MW)+7.571 can be used to estimate GA with a CI of 2.17.

CONCLUSION

The growth of the mandible, maxilla, zygomatic bone and orbits was measured and the corresponding growth curves were established. Several measurements were strongly correlated with gestational age.

Embryonic Heart Rate and Age

This study used linear regression analysis to show that embryonic heart rate (EHR) can be used in the clinical setting to provide an estimate of embryonic age that correlates well with the fetal crown-rump length age (CRL; r = 0.856). A regression was performed on data from 275 examinations in which an embryonic heart rate was recorded before the ninth menstrual week from a cross-sectional population of 1,136 examinations throughout pregnancy. In this analysis, EHR was used as the independent variable and CRL as the dependent variable to yield the following formula for CRL age in menstrual days: CRL Age (menstrual days) = 8.18 + 0.285 EHR. Based on this result, a rounded version of the formula was sought that would provide essentially the same estimated fetal age as the regression formula for the range of EHR that occurred in the sample (84-193 beats/min) yet allow for a simpler computation. Within that range of EHR, the following clinical versions of the regression formula were found to produce results that did not differ significantly from the original formula: Days of Gestation = 0.3 EHR -8 and Menstrual Days Age = 0.3 EHR + 6. Both the original regression and the clinical versions yielded 95% prediction intervals of approximately ± 8 days across the range of EHR that occurred in the sample. While fetal age based on this method is only an approximation of the CRL age, the heart rate can be obtained using time/motion mode sonography when only the less accurate gestational sac diameters are available. The EHR is useful to corroborate early age estimates, especially when using transvaginal transducers and may provide useful information concerning cardiac development.

Craniofacial and neck anomalies

The evaluation of the craniofacial region is a multistep process. First, sonographic skill and expertise are required to ascertain these often subtle abnormalities. Next, precise measurements must be obtained in appropriate and reproducible planes. Finally, a thorough search for other related fetal anomalies is essential. Exciting breakthroughs in our understanding of underlying courses and mechanisms can now guide the practitioner not only in deciding whether or not to pursue invasive testing, but which tests to order, particularly if molecular diagnosis may be required. Complementary advances in ultrasound technology, prenatal diagnosis, and genetic research will have the potential to enhance the accuracy of our counseling, management, and overall care of our patients.

New approaches to human facial morphology using automatic quantification of the relative positions of the orbital and nasal apertures

The purpose of this study was to define and quantify the relative positions of the orbital and nasal apertures in the human face. The material consisted of 44 skulls (32 males, 12 females). For each skull, an image of the projection of the face was captured perpendicular to the palatal plane, using a CCD camera. The orbital and nasal apertures were segmented and characterized using classical image analysis procedures. New quantitative parameters were automatically determined from the centres of area of the facial apertures, and from horizontal and vertical lines of reference. Sexual differences were only significant for orbital height, nasal height, and orbitonasal height. A medio-lateral orbitonasal overlap, as well as a vertical orbitonasal overlap, existed in all individuals; the vertical overlap was always much more marked than the medio-lateral overlap. Significant proportions of the human face were also demonstrated: on average, the interorbital breadth corresponded to a fifth of the biorbital breadth, and thus to half of the mean orbital breadth; the nasal breadth corresponded to one fourth of the biorbital breadth, and the vertical orbitonasal overlap to one fourth of the orbitonasal height. Some instructive significant correlations were observed between these new parameters. The applications of the present methodology seem of great potential interest in anthropology and clinical biometry.

Measurement of facial growth in the human fetus

BACKGROUND

The fetal face is clearly seen by ultrasonography: we considered measurement of certain orbitofacial parameters of interest in the human fetus in order to establish norms for facial development.

METHODS

We included 108 "normal" fetuses ranging in age from 16.5 to 41 weeks of amenorrhea. The orbitofacial parameters studied were outer canthal distance, inner canthal distance, oropalpebral distance right side and left side, and palpebral fissure length side and left side. The ocular parameters studied were corneal horizontal diameter and axial length. The traditional anthropometric parameters of the fetus were determined by pathological examination: age, weight head circumference and height. A statistical study analyzed the different correlations and established linear regression equations for orbitofacial parameters as a function of age. Polynomial regression models were tested to the third degree as a function of age and the head circumference/II ratio.

RESULTS

Results are given in six different age groups. We find excellent correlation between the different parameters. Statistically valid linear regression equations were established for orbitofacial parameters. Polynomial regression equations were compared to linear equations their correlation coefficient and standard error, but showed no greater validity. Skull growth is more rapid than facial growth, which itself is more rapid vertically than horizontally.

CONCLUSION

This study establishes norms for the different orbitofacial parameters, in particular the oropalpebral distance, for which we found no bibliographic references. The general interest of these measures lies in the description of malformation syndromes.

Prenatal diagnosis of isolated bilateral microphthalmia with confirmation by evaluation of products of conception obtained by dilation and evacuation

We describe the prenatal diagnosis of isolated bilateral fetal microphthalmia in a woman at increased risk of having a fetus with microphthalmia. Ultrasound examinations at 16.1 and 19.5 weeks' gestation demonstrated bilateral fetal microphthalmia with no other associated structural defects. The patient elected to terminate her pregnancy at 19.5 weeks. Pathological evaluation of the products of conception obtained by dilation and evacuation confirmed the prenatal diagnosis of isolated bilateral fetal microphthalmia.

Fetal sacral length in the ultrasonographic assessment of gestational age

OBJECTIVE

Our purpose was to establish a nomogram of fetal sacral length throughout gestation and to assess its value in cases of abnormal fetal growth.

STUDY DESIGN

A prospective cross-sectional study of 506 singleton fetuses with normal growth between 15 and 41 weeks' gestation was performed. Regression analyses were performed on sacral length, gestational age, biparietal diameter, head circumference, and femur length. The sacral length in 80 singleton gestations with abnormal growth (40 > 90th percentile and 40 < 10th percentile for gestational age) were compared with the nomogram.

RESULTS

Linear relationships between gestational age and sacral length, biparietal diameter, head circumference, and femur length were demonstrated. Sacral length (centimeters) as a function of gestational age (weeks) was expressed by the regression equation: Sacral length = -0.108 + 0.102 Gestational age, with a Pearson correlation coefficient of R2 = 0.959. The sacral length of all 80 fetuses with abnormal growth demonstrated the same relationship to gestational age as did the 506 normal controls.

CONCLUSION

This study defines the normal limits of sacral length; demonstrates a high correlation between sacral length, gestational age, and other standard measurements of fetal growth; and indicates that sacral length can predict gestational age, irrespective of fetal nutritional status.

Fetal binocular distance as a predictor of menstrual age

The relation between fetal binocular distance and menstrual age was determined by cross-sectional analysis of 555 normal fetuses (14-40 weeks) using real-time sonography. Mathematical modelling of the data demonstrated that the binocular distance growth curve, similar to the biparietal diameter, is nonlinear. Predicted binocular values at various points in gestation were comparable to the results of other investigators. Predicted menstrual age in weeks for specific binocular distance measurements in millimeters were calculated and are reported in tabular form. The variability (+/- 2 SD) associated with predicting menstrual age from binocular distance is +/- 14 days between 14 and 27 weeks, but between 29 and 40 weeks the variability is +/- 24 days. Binocular distance can be used as an adjunct in estimating menstrual age and may be useful in the diagnosis of some abnormalities, e.g. hypotelorism or hypertelorism.