Predicting the sex of fetus in first trimester based on the crown-rump length

Jacek Borowski, Julia Borowska, Anna Szczepańska-Przekota, Agata Walaszczyk, Marek Bulsa


Introduction: Ultrasound examination of pregnant women to assess the anatomy and normal developmental parameters of the fetus has been a standard in obstetrics since the 1980s. Nowadays, attempts are being made to identify sex in early pregnancy. The method of fetal sex determination based on cytogenetic evaluation of fetal cells isolated from maternal blood and free fetal DNA detectable in pregnant women’s blood, developed in recent years, requires a specialised laboratory. In view of these conditions, it seems obvious and necessary to search for alternative methods of fetal sex determination at the earliest possible stage of pregnancy. Therefore, the aim of the present study was to determine the sex of the fetus in the I trimester of pregnancy.
Materials and methods: The initial study included 187 pregnant women who were between 5–10 weeks of gestation (model 1) and the actual study included 240 subjects who were between 5–13 weeks of singleton pregnancy (model 2). A logistic regression model was used to assess the probability of fetal sex based on crown-rump length (CRL), gestational sac volume (GSV), and gestational age.
Results: The study indicates that the sex of the fetus can be predicted with a high probability from ultrasound earlier than previously thought.
Conclusions: After 7 weeks of gestation, differences in the size of male and female fetuses start to become apparent. Male fetuses have on average higher CRL and GSV than female fetuses. This allows predicting male  sex with a significantly higher probability.


crown-rump length (CRL); gestational sac volume (GSV); sex of fetus; I trimester; ultrasonography

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