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Fetal Development

External and Internal genital organs

Fetal genitals nub development


External genital changes in Fetus development

42 days (6 weeks) after fertilization, around week 8 of pregnancy
6 week old embryo (Embryo size = 0.5 inch, 12 mm) 

  1. Buds of the arm
  2. Arc branchial
  3. Placenta membrane
  4. Eye
  5. Genital tuber
  6. Site of the heart
  7. Bud of the leg
  8. Tail
  9. Umbilical cord

 week5 embryo
At the sixth week the site of the genitals is a small bud, called the genital tuber.

Until the ninth week of fetus development, the embryonic reproductive apparatus is the same one for the two sexes.

[ Internal genital organs ]

The Ultrasound Angle of the Dangle
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9 week old embryo  -  11 weeks Pregnant

( Embryo size = 1.75 inch, 45 mm )

week9 male
1. Anus
2. Labioscrotal folds
3. Legs
4. Genital tuber
7. Urethral groove
8. Urogenital folds

At the ninth week, there are not yet any notable differences.

The boy is on the left and the girl on the right. You find the same structures on both fetus.

week9 female
Boy Girl



How big is fetus at 12 weeks pregnant?

[ Mouse Over Image ]
Size at 12 weeks Pregnant At 12 weeks pregnant the fetus will be about 45 to 50 millimeters (less than 2 inches) CRL (head to butt) length, thats just a little more than the width of two U.S. pennies (one cent coins).

The genital tubercle (nub) area at 12 weeks pregnant will be about the size of a 'pin head'. On ultrasound scans; looking through, layers of skin, womb and amniotic fluid it will be difficult to see.

Waiting until 16 weeks pregnant when the fetus is about three times bigger and gender changes done is a better time for that first 'look'.



Male - 11 week old fetus - 13 weeks Pregnant

Development of the male external genitalia is dependent upon dihydrotestosterone which is produced by the testes. As the genital tubercle is elongating and growing to form the penis, the urogenital folds which lie on either side of the urogenital membrane begin to move towards each other forming a groove, this is known as the urethral groove. The urogenital folds fuse together on the ventral side of the developing penis, enclosing what will now become the spongy urethra.

11 week old fetus ( Fetus size = 2.5 inch, 64 mm )
week11 male With a boy, the genital tuber will form the glans penis (4). The body of the penis will be formed by the fusion of the urogenital folds, this fusion is not yet completely finished (7). The scrotum (6) is formed by the fusion of the labioscrotal folds (2). The Raphe [line] of the scrotum (5) corresponds to the zone of fusion of the labioscrotal folds.

At this stage of development, the testicles are located in the abdomen. They will not go down into the scrotum (6) until about the seventh or eighth month of pregnancy.

The foreskin is formed in the twelfth week of development.


Female changes

In the absence of the SRY gene, of the Y chromosome, a female embryo will develop.

The development of the female external genitalia is promoted by the presence of estrogen and other hormones within the maternal system. The phallus described earlier continues to grow to become the clitoris. Meanwhile, the urogenital folds are developing into the labia minora. Their development is similar to that in the male. They grow up along side the phallus except that in the female, they fuse only at the most posterior aspect (bottom) to form the frenulum labiorum pudendi or fourchette.

The labioscrotal folds continue to grow as well, fusing at their most posterior and anterior portions to form labial commissures. The portions of the labioscrotal folds which do not fuse form the labia majora.

13 week old fetus
(fetus size =
3.5 inch, 90 mm)
 17 week old fetus
(fetus size =
5.9 inch, 150 mm)
week13 female
1. Anus
2. Buttocks
3. Clitoris
4. Labia majora [Large lips]
7. Labia minora [Small lips]
6. Legs
week17 female
Girl Girl

20 week old fetus (Fetus size = 7.25 inch, 185 mm)
week20 female

With girls, the genitals are formed starting from the same embryonic bodies as those which form the male reproductive apparatus.

The urogenital and labioscrotal folds are not joined as with boys. They will respectively form the Labia minora (7)[small lips] and Labia majora (4) [large lips] of the vulva. The genital tuber will form the clitoris (3).

Ovaries are not identifiable until after the twelfth week. In girls, the ovaries contain over six million eggs, this decreases to approximately one million by birth and will be reduced to about 400 by the time of puberty.


21weeks male

genitals xy
 By the 20th week of pregnancy the external genitalia changes are done. On ultrasound, if your baby is cooperating and is positioned in a favorable way, his or her sex can be identified as early as the 16th to 18th week of your pregnancy.

week20 maleThe male fetus may show a round bulbous area within the genital area which is the scrotum and penis. This sometimes can be seen on screen as an appearance similar to the profile of a small snail.

Of course, if your baby is 'hiding his stuff' (positioned in such a way as to prevent identification), it will make no difference how far along in your pregnancy you are -- you won't find out your baby's sex.

The correct visualization of any fetal part depends on many factors such as fetal position, amount of amniotic fluid and thickness of the abdominal wall.

3D scans can make it easier to see the gender of baby.

week20 female

genitals xx
 Most of the time the sonographer should be able to tell the sex of the baby by about 20 weeks of pregnancy.

The correct visualization of any fetal part depends on many factors such as fetal position, amount of amniotic fluid and thickness of the abdominal wall.

week20 femaleThe absence of the penis must not be taken as sufficient evidence of the fetus being a girl. Using ultrasound the 3 lines sign which denotes the labia in the fetus is an indication of the female gender.

Ultrasound scans done in later pregnancy or 3D scans can make it easier to see the gender of a baby. The sonographer may not always get a good view of the private parts of the fetus for many reasons and therefore may not be able to give you an accurate answer.

Some sonographers are not allowed to tell you the gender, but may show the genital area on the screen and let you decide which sex your baby is.

[Internal genital organs]


The HOT topic on pregnancy forums around the world is...

The angle of the dangle topic

Q.  Can they tell the sex of baby at 12 week scan ?
A.  At around 12 weeks a sonographer may make a 'best guess' as to the gender of baby from a scan, but this can, and will be, only a little better than 50/50.
12 Week Scan
Mouseover  =  Rotate image

The correct visualization of any fetal part depends on many factors such as fetal position, amount of amniotic fluid and thickness of the abdominal wall. The following images are not typical, as intermediate forms exist, establishing gender can sometimes be very difficult.


Angle of the dangle

On ultrasound, if your baby is cooperating and is positioned in a favorable way, fetal sex can be determined during a scan when the fetus is about 12 weeks (about 14 weeks after LMP).

The determination is made by studying the angle between the genital 'bump' and the direction of the lower portion of the spine. The following images are not typical and intermediate forms do exist, establishing gender can sometimes be difficult.
12 week old fetus - (Fetus size = 3 inch, 75 mm) - 14 weeks pregnant
Male gender
Male 11weeks

With the male fetus, the genital tubercle usually creates an angle of greater than 30° with the lower part of the spine.

Male 11 weeks

Male 12 weeks
 Female gender
Female 11weeks

In the female fetuses, the genital tubercle protrudes in the same direction as the lower portion of the spine with an angle of less than 30° relative to the backbone.

Female 11 weeks

Female 12 weeks


How accurate are routine first trimester scans for fetal gender determination.

Ultrasound gender study - Objective study to assess the accuracy of fetal gender determination at a routine first trimester scan for detailed assessment of anatomy and nuchal thickness measurement.

In the study the angle of the genital tubercle was used to assign fetal gender. At 11 weeks there was an error rate of 50% and only 14 of every 100 was assigned correct male gender. In the male fetuses after 12 weeks, there was a significant increase in the angle of the genital tubercle from the horizontal. The accuracy of sex determination increased with gestation.



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The gender prediction test result is easy to read!   The control test window will change color to either pink (Girl) or blue (Boy).

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