| Summary: | The study was conducted to determine the desirability or otherwise of mathematically correcting every normal foetal head shape to an ideal shape prior to dating using the biparietal diameter (BPD). Transabdominal Sonography was performed in 118 pregnant women in their second- and third- trimesters. The BPDs and fronto-occipital diameters (FODs) were measured. A study of 100 foetuses with normal head shapes was used to derive in this environment, a regression equation for an area corrected BPD (BPDa): BPDa = - 2. 853 + 0.483 (BPD + FOD). The BPDa of 18 foetuses with normal head shapes, were computed with this equation. Z test was performed to compare the mean BPD and Mean BPDa. Z statistic showed no significant difference (p>0.5) between BPDa and BPD in this group of foetuses with normal head shapes. There is no need to mathematically correct normocephalic foetal head shapes to ideal shapes before dating using the BPDs
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