Female external genitalia on fetal magnetic resonance imaging

• Published in: Ultrasound in obstetrics & gynecology Vol. 38; no. 6; pp. 695 - 700
• Main Authors: Nemec, S. F., Nemec, U., Weber, M., Rotmensch, S., Brugger, P. C., Kasprian, G., Krestan, C. R., Rimoin, D. L., Graham, J. M., Prayer, D.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-12-2011; Wiley; Wiley Subscription Services, Inc
• Subjects: Adolescent; Adult; bilabial diameter; Biological and medical sciences; Data processing; external genitalia; Female; female sexual development; fetal MRI; Fetuses; genital abnormalities; Genitalia; Gestational Age; Gynecology; Gynecology. Andrology. Obstetrics; Humans; Magnetic Resonance Imaging; Mathematical models; Medical sciences; Middle Aged; Obstetrics; Pregnancy; Prenatal Diagnosis - methods; Reference Values; Regression analysis; Retrospective Studies; Sexual Development - physiology; Statistical analysis; Statistics; Time Factors; Ultrasound; Vulva - abnormalities; Vulva - embryology; Young Adult; external genitalia; Sexual development; Gynecology; Genital system; Nuclear magnetic resonance imaging; Obstetrics; female sexual development; Pregnancy; genital abnormalities; fetal MRI; Prenatal diagnosis; External; Medical imagery; Female; Fetus; bilabial diameter; Diameter
• ISSN: 0960-7692; 1469-0705; 1469-0705
• DOI: 10.1002/uog.8973

Objectives
To characterize the normal development of the female external genitalia on fetal magnetic resonance imaging (MRI).
Methods
This retrospective study included MRI examinations of 191 female fetuses (20–36 gestational weeks) with normal anatomy or minor abnormalities, following suspicion of anomalies on prenatal ultrasound examination. Using a 1.5‐Tesla unit, the bilabial diameter was measured on T2‐weighted sequences. Statistical description, as well as correlation and regression analyses, was used to evaluate bilabial diameter in relation to gestational age. MRI measurements were compared with published ultrasound data. The morphological appearance and signal intensities of the external genitalia were also assessed.
Results
Mean bilabial diameters, with 95% CIs and percentiles, were defined. The bilabial diameter as a function of gestational age was expressed by the regression equation: bilabial diameter = − 11.336 + 0.836 × (gestational age in weeks). The correlation coefficient, r = 0.782, was statistically significant (P < 0.001). Bilabial diameter on MRI was not significantly different from that on ultrasound (P < 0.001). In addition, on MRI we observed changes in morphology of the external genitalia and in signal intensities with increasing gestational age.
Conclusions
We have provided a reference range of fetal bilabial diameter on MRI, which, in addition to ultrasound findings, may be helpful in the identification of genital anomalies. Copyright © 2011 ISUOG. Published by John Wiley & Sons, Ltd.