Normal sexual differentiation is a complex process. In the first six weeks of gestation, human development in the two sexes is identical in a potential state. The upcoming development of the external genitalia into male or female structures ends by week 12 in the male and later in the female. Women First GYN offers gender reveal in Chesapeake using ultrasound, helping parents better prepare for their unborn babies.

Regarding the external genitalia, three organs exist before differentiation: the genital swelling or labio-scrotal swelling, the genital folds, and the genital tubercle. In males, the testes produce testosterone which is reduced to dihydrotestosterone which acts on the external genitalia, resulting in their anterior displacement, a fusion of the labio-scrotal folds to form a scrotum, and fusion of the genital folds developing into the penile shaft. The genital tubercle forms the glans penis in males.

In the female, the labio-scrotal 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.  An old study done in 1989 was the first to describe the sagittal sign for determination of fetal sex in early gestation.

The fetus is scanned in the midline sagittal plane, following the ramp from dorsal to ventral, the focal bulge representing the penis or clitoris ventrally. The penis appears as an anteriorly directed bulge, while the clitoris appears as a caudally directed bulge.

Another method to differentiate male from female early in pregnancy is by drawing a line through the genital tubercle that intersects with another line along the skin surface of the lumbosacral spine in the mid-sagittal plane. This denotes a male fetus if the angle is greater than 30 degrees with an anteriorly directed genital tubercle. This denotes a female fetus if the angle is less than 10 degrees with a caudally directed genital tubercle, but if the angle is between 10 and 30 degrees, this is indeterminate.

In another study, the sonographic determination of male genitalia was based on identifying a non-septate dome-shaped structure at the base of the penis called dome sign, indicating the scrotum. Female external genitalia is based on the visualization of the 3-lines sign, representing the labia majora and more.

Better visualization of the fetal sex is in the second trimester than the first trimester, and gender determination can rely on the visualization of the penis and scrotum themselves in males and on the 3-lines sign of labial lines in the female.

Sometimes it is easy to know a boy or girl, but sometimes that is not easy. So, what your care provider will do if they cannot see the external genitalia or they are ambiguous is assess the internal reproductive organs. Direct visualization of the uterus or the testicles would be the way to go. Testicles do not descend to the scrotum before 25 weeks of gestation. By 32 weeks, bilateral testicular descent is observed in 97% of cases. The fetal ovaries are visualized as early as 19 weeks of gestation. The uterus is seen with the mean transverse diameter increased from six millimeters at 19 weeks to 20 millimeters at 38 weeks.

Schedule your ultrasound gender reveal appointment with Women First GYN to receive accurate sex determination of your fetus. 

Author's Bio: 

Marina Pal is a renowned author and social media enthusiast.