Joined on 06-23-2009
Yay! At 11 weeks both boys and girls look about the same but by 13 weeks there is often a pretty discernible difference. By 15 weeks there's no mistaking it.
9 week old embryo - 11 weeks Pregnant
|( Embryo size = 1.75 inch, 45 mm )|
|1. Anus |
2. Labioscrotal folds
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.
How big is fetus at 12 weeks pregnant?
[ Mouse Over Image ]
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
|11 week old fetus|| ||( Fetus size = 2.5 inch, 64 mm )|
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. |
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.
|Boy|| || |
|In the absence of the SRY gene, of the Y chromosome, a female embryo will develop. |
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
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)
4. Labia majora [Large lips]
7. Labia minora [Small lips]
|20 week old fetus|| ||(Fetus size = 7.25 inch, 185 mm)|
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).
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