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in this short talk we will discuss how to determine normal fetal gender and how to differentiate male from female fetus as we all know normal sexual differentiation is a complex process in the first six weeks of gestation human development in the two sexes is identical in a bipotential state subsequent development of the external genitalia into the characteristic male or female structures is completed by week 12 in the male and later in the female so as regarding the external genitalia three organs exist before differentiation the genital swelling or labioscrotal swelling the genital folds and the genital tubercle in males the testes produce the testosterone which is reduced to dihydrotestosterone dihydrotestosterone acts on the external genitalia this results in their anterior displacement fusion of the labial scrotal folds to form a scrotum and fusion of the genital folds to form the penile shaft the genital tubercle forms the gland's penis in males in the female the labioscrotal folds form the labia majora the genital folds form the labia minora and the genital tubercle forms the clitoris determination of normal fetal gender by visualization of external genitalia intrauterine sex determination is performed by ultrasound evaluation of the external genitalia from the second trimester onwards old study done in 1989 was the first to describe the sagittal sign for determination of fetal sex in early gestation with the fetus being scanned in the midline sagittal plane following the rump from dorsal to ventral the focal bulge representing the penis or clitoris can be seen ventrally the penis appears as anteriorly directed bulge while the clitoris appears as codley directed bulge on the image here on the right side of the screen as you can see this is 12 weeks gestation if we follow the rump from dorsal to ventral we can see the genital tubercle is directed anterior denoting male fetus on the other image on the left side of the screen the genital tubercle is seen directed cuddly or downwards denoting female fetus another method to differentiate male from female early in pregnancy is by drawing a line through the genital tubercle intersects with another line along the skin surface of the lumbosacral spine in mid-sagittal plane if the angle is greater than 30 degrees with anteriorly directed genital tubercle this denotes male fetus if the angle is less than 10 degrees with caudally directed genital tubercle this denotes female fetus but if the angle is between 10 and 30 degrees this is indeterminate here is an image at 12 weeks of gestation the genital tubercle is directed anteriorly with the angle more than 30 degree denoting male and on the other image the genital tubercle is directed cuddly with the angle less than 10 degree denoting female look at these two images on the image here on the right side of the screen as you can see the genital tubercle is directed codley denoting female fetus on the other image on the left side of the screen the genital tubercle is directed anterior denoting male fetus in another study the sonographic determination of male genitalia was based on identification of a non-septate dome-shaped structure at the base of the penis called dome sign and this indicating the scrotum female external genitalia were identified based on the visualization of three-line sign representing the labia majora and menorah better visualization of the fetal sex can be achieved in the second trimester than first trimester and gender determination can rely on visualization of the penis and scrotum themselves in males and on the three-line sign of labial lines in the female as you can see on the upper images the penis is seen connected to dome-shaped structure of the scrotum in male fetuses while in the lower images the three-line sign of labial lines are better visualized denoting female fetus the penile length can be measured into uterine it is measured from the scrotal edge to tip of the glands in a study published in 2001 the mean penile length at 14 weeks of gestation was about 3.8 millimeters and reaches up to 23.7 millimeters at 38 weeks sometimes it is easy to know boy or girl but sometimes that is not easy so what we do if we cannot see the external genitalia or they are ambiguous the first thing is to go on and assess the internal reproductive organs and direct visualization of the uterus or the testicles would be the way to go testicles do not descend to the scrotum prior to 25 weeks of gestation by 32 weeks bilateral testicular descent was observed in 97 of cases the fetal ovaries can be visualized as early as 19 weeks of gestation the uterus can also be seen with the mean transverse diameter increased from 6 millimeters at 19 weeks to 20 millimeters at 38 weeks on the image on the right side of the screen we can see two testicles fully descended in this term male fetus on the other image we can see the urinary bladder and the uterus is seen anterior to rectum with the endometrium well visualized in a female fetus on this image we can see this is a sagittal view of a fetus the uterus is seen seated anterior to the rectum and posterior to the urinary bladder in a female fetus measurement of rectovesical interspace the presence of the uterus in female fetuses results in increase the distance between the urinary bladder and rectum as compared to male fetuses measuring the distance between the posterior wall of the bladder and the anterior wall of the rectum allowed us to determine fetal sex correctly between 14 and 40 weeks of gestation so recto vesicle interspace is the distance between the anterior wall of the rectum to the posterior wall of the urinary bladder it is measured in axial plane at the level of umbilical arteries in cross section at mid urinary bladder practically if the distance is greater than five millimeters then it indicates female fetus as you can see in these images the rectovesical interspace in female fetus is much more greater than in male fetus another method to differentiate male from female is by looking at the interface of rectovesical interspace with the posterior wall of the urinary bladder if this interface is concave it indicates female fetus if this interface is convex this denoting male fetus so on image on the right side of the screen the interface with the urinary bladder is concave denoting female fetus on the image on the left side of the screen this interface is convex and this denoting male fetus take home points development of the external genitalia into the characteristic male or female structures is completed by week 12 in the male and later in the female sagittal sign is helpful sign for determination of fetal sex in early gestation if the genital tubercle is anteriorly directed it denotes male fetus if caudally directed it denotes female fetus measuring the angle between the genital tubercle and lumbosacral skin surface is helpful for determination of fetal sex in early gestation testicles do not descend to the scrotum prior to 25 weeks of gestation and fetal ovaries can be visualized as early as 19 weeks of gestation measuring the rectovesical interspace and assessing the interface with the urinary bladder can differentiate male from female fetus thank you for your attention