All eggs contain one X chromosome, while sperm contain either an X chromosome or a Y chromosome. Embryos with XY chromosomes develop male sex organs, while those with XX chromosomes develop female sex organs. That means that our sex organs come from the same foundations: The testes in men are equivalent to labia and ovaries in women, and the penis is the equivalent of the clitoris.
At around week 7 , male genitalia begin to develop when the Y chromosome signals for the start of testosterone production. The genital ridge starts lengthening to form the penis. The penis and clitoris, however, actually remain the same size until about 14 weeks. In a baby boy, buds that will become the prostate appear at around 10 weeks , and his urinary system is fully formed by about 14 weeks.
Between 16 and 20 weeks, testosterone levels fall until they reach the range found in early puberty by about 24 weeks. In girls, the ovaries will first appear around weeks 11 to 12 of pregnancy. And by about week 20 , a baby girl will have somewhere near 7 million primitive eggs. At around 18 to 22 weeks of pregnancy, a level 2 anatomy ultrasound can commonly determine whether a baby is male or female by looking for a penis, although technicians do occasionally make the wrong call.
An ultrasound done at 13 weeks — usually as part of the nuchal translucency screening — can also give a very good clue as to your baby's sex. Intersexuality can stem from a range of factors, and in some cases the cause is unknown.
The most common cause is not having a clear pair of XY or XX chromosomes. Rare disorders such as Turner syndrome, Klinefelter syndrome and androgen insensitivity syndrome are among numerous other causes. If testosterone is not present, female organs will develop, making female the "default sex" for human beings. Although your baby's gender is determined immediately upon fertilization, you will not be able to know the sex until about the 16th to 18th week of pregnancy.
At around the sixth week your baby will develop a small bud called the genital tuber at the site of the genitals. This will look the same for boys and girls until around the 9th week when the sex organs begin to form. By the end of the 20th week, the external sex organs should be fully formed for both male and female babies. According to the Intersex Society of North America ISNA , "intersex" is a term used to describe a variety of conditions in which a person is born with a sexual anatomy that doesn't fit typical definitions of male or female.
For instance, a person may be born with genitals that are in between usual male and female parts or may be born with both XX and XY chromosomes. The ISNA says to understand intersex, think of gender like the color spectrum.
Sex organs vary in shape and size and sex chromosomes can vary as well. While most cultures divide people into male and female categories, this is not the way of nature. This condition is very rare but it does exist. The word "gender" has become quite controversial. If the fetus has an unusual level of certain hormones, or an unusually high or low ability to respond to them, then an in-between genital appearance can result. These diagrams show some of the ways genitals can look when a child is born.
Most boys are born with genitals looking something like the diagram numbered 1. Most girls are born with genitals looking something like the diagram numbered 6. Sometimes children are born with genitals that look like the other pictures.
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