SEX DIFFERENCE IN CROWN-RUMP LENGTH IN FIRST-TRIMESTER TWINS

OBJECTIVE: To determine if there is a difference in the crown-rump len gth (CRL) between male and female fetuses in the first trimester. STUD Y DESIGN: CRL was determined in 77 normal twin pairs at the time of ch orionic villus sampling. The sex of each fetus was assigned based upon the results of the sampling. RESULTS: A small difference was found be tween the CRL of males as compared to females, but this teas not stati stically significant. However, if there was a difference in size betwe en the twin pairs, the odds were 1.5:1 that the larger would be male. CONCLUSION: There is no clinically significant difference in size betw een male and female fetuses in the first trimester of pregnancy.