Biparietal diameter: Significant gender difference is present in later weeks of gestation

Abstract

Objective: Objective of this study was to find the presence and significance of difference in biparietal diameter values of male and female fetuses of local population at 35 weeks of gestation. Material & methods: Study was conducted at Lahore General Hospital, and partly in Sir Ganga Ram Hospital/Fatima Jinnah Medical College, Lahore, Pakistan in the year 2005. Outer to inner biparietal diameter in 60 normal singleton fetuses was measured at 35 weeks of gestation. Among them 30 fetuses were male and 30 females. All had comparable values of femur length and fetal abdominal circumference. Mean BPD and standard deviation were calculated for the total, male and female groups separately. Results: Mean BPD in total 60 patients was 87.1mm, SD2.6. Mean BPD of male group was 88.4mm, SD2, while that of female group was 85.9mm, SD2.4. Lower limit of 2SD range was accordingly different. When lower 2SD limit of male group was used, significant (P<0.05) number (23%) of female fetuses showed BPD<2SD. Using common mean and SD, 13% females showed BPD<2SD, while use of female specific mean and SD showed normal distribution. Conclusion: Biparietal diameter values at 35 weeks of gestation are significantly different in fetuses of each sex. Mean BPD of female fetuses at 35 weeks is 2mm shorter than mean BPD of male fetuses of same age. Male fetuses have a relatively narrow range of normal BPD; and this parameter can be used in males for reliable estimation of gestational age. Females have relatively wider range of normal BPD. Female BPD seems to be responsible for wider range of common nomograms. This parameter alone should not be used for age estimation or diagnosis of small for dates, or microcephaly, in later weeks of gestation in females. Gender specific BPD nomograms may improve the prenatal assessment of fetal growth and structural anomalies.