Normal value of cephalic index and craniotypes: a pilot sonographic cephalometric survey of pregnant women of Yoruba ethnic origin in Lagos, southwest Nigeria
Keywords:Fetus, simple regression, Bland-Altman plot, craniometry
Background: Sonographic cephalometry is used to identify ethnic differences. Biparietal diameter (BPD) and occipito-frontal diameter (OFD) may be used to compute cephalic index (CI).
Methods: A sonographer measured the BPD and OFD in 200 pregnant women of Yoruba ethnic origin. The formula BPD/OFD x 100 was used to compute the CI. Mean CI was used to determine craniotypes. Coefficient of correlation, line graph, and the Bland-Altman plot, were used to determine the relationship between CI, BPD and OFD.
Results: Mean CI was 77.24 Â± 3.88 mm. There was a statistically significant difference (p < 0.05) in mean CI between fetuses of Yoruba, Igbo and Indian ethnic origin. Correlation was significant between CI and BPD (r = 0.163; p = 0.02) and between CI and OFD (r = -0.02; p = 0. 000); 68.0% of fetuses had mesocephaly. The formula CI = 0.0371(BPD) + 74.656 and CI = 0.0035 (OFD) + 77.559 may be used to calculate CI on the basis of respective sonographically measured BPD and OFD.
Conclusion: While the skull appeared to have grown to its full length and breadth in the first trimester of pregnancy, a typical fetus of Yoruba ethnic origin in Lagos metropolis most likely would have a long and flat skull at birth. Even as ethnic differences appear to be a major factor in the development of cranial development in the population studied, a simple regression equation can be used to compute cephalic index and to correct atypical craniotypes among fetuses without craniofacial anomalies.
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