First-trimester determination of fetal gender by ultrasound: measurement of the ano-genital distance.
BACKGROUND
Early ultrasound fetal sex determination is of obvious interest, particularly in the context of X-linked diseases. In the human, the anogenital distance, i.e., the distance between the caudal end and the base of the genital tubercule is sexually dimorphic. This difference is apparent from 11 weeks of gestation. The aim of this prospective study was to evaluate the accuracy of anogenital distance measurement during the first trimester ultrasound in the early determination of fetal gender.


METHODS
Fetal gender was assessed by ultrasound in 310 singleton pregnancies at 11-14 weeks of gestation. The optimal cut-off was determined by the minimal p-value technic and validated using bootstrap simulation.


RESULTS
310 women were included. A cut-off of 4.8mm was determined to predict male (≥4.8mm) or female (<4.8mm) fetuses. Sex was correctly determined for 87% of the males and 89% of the females. The inter-observer variability was excellent.


CONCLUSIONS
This study presents a new sonographic sign for early fetal sex determination that has not been previously explored. It appears to be an accurate tool but it requires further validation in larger series.
Department of Obstetrics, Gynecology and Reproductive Medicine, Hôpital Tenon, Assistance Publique des Hôpitaux de Paris, Université Pierre et Marie Curie Paris 6, GRC 6-UPMC Centre Expert en Endométriose (C3E), France. Electronic address: alexandra_arfi@wanadoo.fr.
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Arfi
Department of Obstetrics, Gynecology and Reproductive Medicine, Hôpital Tenon, Assistance Publique des Hôpitaux de Paris, Université Pierre et Marie Curie Paris 6, GRC 6-UPMC Centre Expert en Endométriose (C3E), France.
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Cohen
Department of Obstetrics, Gynecology and Reproductive Medicine, Hôpital Tenon, Assistance Publique des Hôpitaux de Paris, Université Pierre et Marie Curie Paris 6, GRC 6-UPMC Centre Expert en Endométriose (C3E), France.
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Canlorbe
Department of Obstetrics, Gynecology and Reproductive Medicine, Hôpital Tenon, Assistance Publique des Hôpitaux de Paris, Université Pierre et Marie Curie Paris 6, GRC 6-UPMC Centre Expert en Endométriose (C3E), France; ISERM UMRS 707, « Epidemiology, Information systems, Modeling », University Pierre and Marie Curie, Paris, France.
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Bendifallah
Department of Radiology, Tenon Hospital, AP-HP, Paris, France; GRC6-UPMC: Centre expert en Endométriose (C3E), Paris, France; UMR_S938 Université Pierre et Marie Curie Paris 6, Paris, France.
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Thomassin-Naggara
Department of Obstetrics, Gynecology and Reproductive Medicine, Hôpital Tenon, Assistance Publique des Hôpitaux de Paris, Université Pierre et Marie Curie Paris 6, GRC 6-UPMC Centre Expert en Endométriose (C3E), France.
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Darai
Department of Obstetrics, Gynecology and Reproductive Medicine and Centre Maladies Rares, Hernie de Coupole Diaphragmatique, Hôpital Antoine Béclère, APHP, Université Paris Sud, Clamart, France.
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Benachi
Department of Obstetrics and gynecology, Hôpital Armand Trousseau, Assistance Publique des Hôpitaux de Paris, Université Pierre et Marie Curie Paris 6, France.
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Arfi
D001003:Anal Canal / Q000000981:diagnostic imaging* / Q000196:embryology; D003198:Computer Simulation; D018568:Crown-Rump Length; D005260:Female; D005602:France; D005836:Genitalia, Female / Q000000981:diagnostic imaging* / Q000196:embryology; D005837:Genitalia, Male / Q000000981:diagnostic imaging* / Q000196:embryology; D005865:Gestational Age; D006801:Humans; D059012:Lost to Follow-Up; D008297:Male; D015588:Observer Variation; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011446:Prospective Studies; D012372:ROC Curve; D015203:Reproducibility of Results; D012727:Sex Characteristics; D012732:Sex Determination Analysis; D016216:Ultrasonography, Prenatal
Anogenital distance; First trimester ultrasound; Sex determination