Sex difference in crown-rump length in first-trimester twins

Area of Science:

• Prenatal development
• Fetal sex determination
• Early pregnancy ultrasound

Background:

• Crown-rump length (CRL) is a key biometric parameter in early pregnancy.
• Assessing fetal growth and sex differences is crucial for understanding typical prenatal development.
• Previous studies have explored fetal growth variations, but first-trimester sex-based differences require further investigation.

Purpose of the Study:

• To investigate potential differences in crown-rump length (CRL) between male and female fetuses during the first trimester.
• To establish whether fetal sex is a determinant of CRL in early gestation.

Main Methods:

• Crown-rump length (CRL) measurements were obtained from 77 normal twin pairs.
• Fetal sex was determined using chorionic villus sampling results.
• Statistical analysis was performed to compare CRL between sexes.

Main Results:

• A minor difference in CRL was observed between male and female fetuses, which did not reach statistical significance.
• In twin pairs with a size discrepancy, there was a 1.5:1 odds ratio favoring males as the larger fetus.
• No statistically significant growth disparity was detected based on fetal sex in the first trimester.

Conclusions:

• There is no clinically significant difference in crown-rump length (CRL) between male and female fetuses in the first trimester.
• Fetal sex is not a significant predictor of size during early pregnancy based on CRL measurements.
• These findings support the current practice of using standardized growth charts irrespective of fetal sex in the first trimester.