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Updated: Jul 31, 2026

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Published on: March 28, 2016
Sex difference in crown-rump length in first-trimester twins
N A Ginsberg1, A Cadkin, C Strom
1Department of Obstetrics and Gynecology, Northwestern Memorial Hospital, Chicago, Illinois, USA.
Objective:
To determine if there is a difference in the crown-rump length (CRL) between male and female fetuses in the first trimester.
Study Design:
CRL was determined in 77 normal twin pairs at the time of chorionic villus sampling. The sex of each fetus was assigned based upon the results of the sampling.
Results:
A small difference was found between the CRL of males as compared to females, but this was not statistically significant. However, if there was a difference in size between the twin pairs, the odds were 1.5:1 that the larger would be male.
Conclusion:
There is no clinically significant difference in size between male and female fetuses in the first trimester of pregnancy.
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