PATTERNS OF ORBITOFACIAL AND ORBITAL GROWTH AT PRENATAL STAGE DERIVED FROM FETAL AUTOPSY STUDIES

Objective: Fetal orbitofacial and orbital measurements may be helpful in early prenatal diagnosis of craniofacial malformation. Most of the earlier studies are ultrasound based and there are only a few studies based on fetal autopsies. Comprehensive analysis of various parameters can provide useful database for easy reference. Methods: In fifty normal fetuses of different gestational ages, the following parameters were measured: outer and inner canthal distances, palpebral fissure length, oropalpebral length, depth and width of orbit and inter orbital distance. Results: Statistical analysis revealed significant positive correlation of all these parameters with gestational age and biparietal diameter. The growth patterns of the orbitofacial and orbital measurements also demonstrated significant correlation between these parameters. Conclusion: Our results demonstrate that the lateral parts of the face and the vertical facial length grow at a faster rate than the median part of the face. Deviations from the normative data generated for the orbitofacial and orbital parameters will help in early detection of specific genetic syndromes.

are ultrasound based and there are only a few studies based on fetal autopsies.Comprehensive analysis of various parameters can provide useful database for easy reference.Methods: In fifty normal fetuses of different gestational ages, the following parameters were measured: outer and inner canthal distances, palpebral fissure length, oropalpebral length, depth and width of orbit and inter orbital distance.Results: Statistical analysis revealed significant positive correlation of all these parameters with gestational age and biparietal diameter.The growth patterns of the orbitofacial and orbital measurements also demonstrated significant correlation between these parameters.Conclusion: Our results demonstrate that the lateral parts of the face and the vertical facial length grow at a faster rate than the median part of the face.Deviations from the normative data generated for the orbitofacial and orbital parameters will help in early detection of specific genetic syndromes.

INTRODUCTION
The study of fetal growth and development by prenatal ultrasound has been facilitated by the availability of anthropometric standards for the fetal body (Escobar et al., 1988).Fetal biometry could be a valuable tool in syndrome delineation and also for distinguishing normal and abnormal craniofacial development (Roelfsema et al., 2007).Such data will not only contribute to a description of facial dysmorphogenesis but will also lead to a better understanding of normal facial growth and development.Craniofacial measurements may prove to be an useful tool for prenatal diagnosis and gestational aging (Escobar et al., 1988).Various craniofacial and orbital fetal measurements at different gestational ages have been described.(Burdi et al., 1988;Denis et al., 1998;Diewert, 1985;Escobar et al., 1988;Escobar et al., 1990;Guihard-costa et al., 2003;Guihard-costa et al., 2006;Kragskov et al., 1997;Roelfsema et al., 2007;Sibert, 1986;Sivan et al., 1997;Wu et al., 2000).Most of these studies are ultrasound based and there are only a few reports based on fetal autopsies.A comprehensive statistical analysis of various facial and orbital parameters is not widely reported.It is desirable that local values derived from well defined population groups be used as a reference in the evaluation of fetuses with dysmorphic facial features in order to avoid errors in diagnosis due to racial variations.(Adeyemo et al., 1998).The present study was designed to generate morphometric data for specific facial and orbital parameters across various gestational ages in fetuses of North-West Indian population.The depth of the orbit was measured at the centre of the orbit.The Width of the orbit was taken at the rim of the orbit.The inter-orbital distance (the distance between the centers of the right and the left orbits) was also measured at the level of the orbital rim.Data was grouped into anthropometric, orbitofacial and orbital groups.Correlations were tested among all parameters by Spearman rank correlation.The growth pattern of orbitofacial and orbital parameters was studied by adjusted r 2 values.

RESULTS
A total of 50 fetuses were studied out of which 27 were females.There was a significant correlation between increase in the gestational age and the increase in weight and BPD.BPD was found to have maximum correlation with age (p=.000).
The height and weight did not correlate significantly with BPD.Therefore in further analysis age and BPD were the parameters against which various orbital and ocular parameters were compared.
The mean values of orbitofacial and orbital parameters on the right and the left side were calculated for each gestational age group.A paired sample correlation test with 95% confidence interval did not demonstrate a significant difference in any of these parameters between the right and the left sides.For further analysis of the results the combined means of the right and left values was used.Gender wise analysis was also done.Means of all studied parameters are given in Table 1.

Orbitofacial parameters
For statistical analysis, Spearman rank correlation was used.There was a significant correlation between increase in gestational age and all the orbitofacial (OCD, ICD, PFL & OPL) parameters (r=.716-.794,p=.000) (Figure 1).Similar significant positive correlation was observed between BPD and all orbitofacial measurements (r=.785-.858,p= .000)(Figure 2).These four orbitofacial parameters also demonstrated significant correlation when compared with each other, in their growth pattern (r=.717-.920,p=.000).Gender wise, among male fetuses similar significant correlations were observed when the increase in gestational age and BPD were plotted against OCD, ICD, PFL and OPL.In females, gestational age correlated well with these orbitofacial parameters with significant p values (p<.01), but no significant correlation was observed between BPD and all the four orbitofacial parameters (r=.288 -.387, p>.05).

Orbital parameters
Again, using Spearman rank correlation with age as an independent variable, the increase in the depth of orbit (DO), width of orbit (WO) and the inter orbital distance (IOD) were correlated with the increase in gestational age (Figure 1).There was significant correlation between age and all the three orbital parameters (r= 0.594-0.711,p=.001).The increase in the DO, WO and IOD also correlated well (r=0.694-0.802,p=.000).
Similarly significant correlation was found between the increase in BPD and the corresponding increase in DO, p=.000).(Figure 2).All these orbital parameters were tabulated separately for males and females.Correlation was calculated in both sexes separately.Among males there was a good correlation between all the orbital parameters with age and BPD.In females, increase in the gestational age correlated significantly with DO (r=0.587,p< .002)and to some extent with IOD (r=0.501,p< .024)but there was no statistically significant correlation with WO (r=0.267,p< .197).When the growth of the BPD was plotted against the orbital parameters in the females no statistically significant correlation was found (r=0.170-0.307, p> .01).However the three orbital parameters correlated well among themselves (r=0.664-0.842, p< .000).
The quantum of increase in different parameters with each gestational week was statistically analyzed to observe the differential growth for each parameter, denoted by r 2 and adjusted r 2 (Table 2).The r 2 changes for OCD were relatively greater than the r 2 changes for ICD and IOD.The parameters PFL and OPL also demonstrated greater r 2 change with increase in each gestational week as compared to IOD and ICD.

DISCUSSION
In recent years enormous progress has been made in the understanding of normal prenatal craniofacial development.Molecular genetics and animal models for studying the role of genetic and environmental factors relevant to fetal malformations have provided insights into abnormal development.(Jhonston and Bronsky, 1995).Parallel to the understanding of genetics and cell migration, there are studies involved in determining growth of fetal facial and orbital structures and their correlation with the corresponding development of the skull (Denis et al., 1998).
Early diagnosis of craniofacial dysmorphic syndromes is directly linked to availability of normative fetal biometric data.As there can be significant racial and ethnic variations, data derived from one population group cannot be extrapolated for establishing deviations from normal fetal measurements in a different population group.The present study has generated morphometric fetal data for various orbitofacial and orbital parameters in North-West Indian population.
In the present study, the orbital as well as orbitofacial growth parameters were determined at different gestational ages (11 th -36 th week).All the parameters had a significant and positive correlation with increase in gestational age and BPD.In addition to age and BPD, orbital and orbitofacial values correlated significantly with each other.The mean values for these parameters at different gestational ages were derived.These would be useful in developing growth charts for the population against which deviation from the normal fetal parameters could be studied.Measurement of orbital and orbitofacial values during routine antenatal ultrasound would thus be extremely useful in diagnosis of craniofacial malformation syndromes and possibly, in future, in utero fetal therapeutic interventions.Different orbital and facial parameters have been measured in utero by antenatal ultrasound.(Escobar et al., 1990;Sivan et al., 1997;Roelfsema et al, 2007) The exact parameters as well as the gestational ages studied vary in different reports.Thus it is not practical to compare absolute fetal measurements from the present study with other ultrasound based studies.In a biometric study of human fetuses from France, a wide range of gestational ages were included, as in the present study.At gestational age 18.5-20 weeks, the OCD, ICD, PFL and OPL were 3.15 cm, 1.27 cm, 0.9 cm and 1.8 cm respectively while in the age group of 25.5-28 weeks values were 4.3 cm, 1.63 cm, 1.34 cm and 2.5 cm.These values are close to the measurements in the present study at approximately similar gestational ages (Table 1).Although the French study does not mention the racial or ethnic sub grouping of the fetuses, our population would be expected to be different.Thus, it is necessary to have region based and population based data across similar gestational ages and measuring the same set of fetal parameters for any meaningful comparison.

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The adjusted r 2 models probably best describe the growth of each parameter.Quantitative growth of each parameter per unit change in gestational age (week wise) was also studied by the regression model and the r 2 changes were calculated.The r 2 changes were more in PFL, OCD and OPL as compared to ICD and IOD.These results demonstrate that the lateral parts of the face (outer canthal distance) as well as vertical facial length (oro-palpebral length) increase at a faster rate as compared to growth of median parts of the face (inner canthal distance and inter-orbital distance) (Fig. 3).Denis et al (1998) asserted that the growth of the skull predominates over that of the face and that the face grows more rapidly along its vertical axis than along its horizontal axis.Vertical growth of the face more closely follows that of the skull as compared to the horizontal growth.Measurement of relative growth rates of the fetal skull and face from numbered contours of photographs and roentgenograms of the head were analyzed by Trenouth (1991).Facial length growth rate was more than that of width.Siebert (1986) also stated that the centre of the face seems to grow slower than the sides of the face and concluded that the transverse growth is probably more rigidly controlled than the sagittal growth.These findings have been corroborated in our study as well.The present study has resulted in generating data about fetal orbitofacial and orbital growth patterns in North-West Indian population.Further work including larger number of fetuses in different gestational ages is desirable to have a higher predictive value.

Table 2 -
Table depicting the quantum of increase in each parameter with unit increase in gestational age (per week).