Objectives: We investigated whether the number of weeks of gestation influences the accuracy of first-trimester fetal sex prediction by analysis of deoxyribonucleic acid extracted from whole maternal blood. A comparison was also made to determine whether a difference exists between this approach and the deoxyribonucleic acid analysis of transcervical cells performed on the same group of subjects.
Study design: Deoxyribonucleic acid was isolated from 50 maternal blood samples taken between gestational weeks 7 and 11. The sex of the fetus was assessed by nested polymerase chain reaction specific for the amelogenin gene. A receiver-operating characteristic curve analysis was used to correlate the accuracy of fetal gender prediction with the gestational age and also to compare the goodness of the 2 methods under investigation.
Results: Analysis of the receiver-operating characteristic curve provided a cutoff value of 9 weeks 4 days of gestation for both tests, indicating that a higher degree of accuracy in the sex assignment was obtained in those samples taken before or at this time. However, this difference was statistically significant only for analysis of deoxyribonucleic acid from maternal blood. The comparison between tests of deoxyribonucleic acid from maternal blood and from transcervical cells showed that the first approach is better, although a statistically significant difference was not found.
Conclusion: Analysis of maternal blood deoxyribonucleic acid is a better approach than analysis of trans-cervical cell deoxyribonucleic acid in fetal sex prediction. The highest degree of accuracy is obtained when blood is drawn before 10 weeks of gestation. This can be important when sampling of chorionic villi should be avoided because of the risk of an X-linked disease when the fetal sex is female.