When is the sex of a fetus determined

NCBI Bookshelf. Sex differences of importance to health and human disease occur throughout the life span, although the specific expression of these differences varies at different stages of life. Some differences originate in events occurring in the intrauterine environment, where developmental processes differentially organize tissues for later activation in the male or female. In the prenatal period, sex determination and differentiation occur in a series of sequential processes governed by genetic and environmental factors. During the pubertal period, behavioral and hormonal changes manifest the secondary sexual characteristics that reinforce the sexual identity of the individual through adolescence and into adulthood.
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How Soon Can You Find Out the Sex of Your Baby?

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When Can You Find Out the Sex of Your Baby? | Parents

Boy or girl? Here's everything you need to know about when you can find out the gender of your baby through ultrasound. This is one of the most common questions doctors get from parents-to-be. The position of the baby during the ultrasound is key, and if your baby's curled up or facing the wrong way, you may have to wait until your next appointment. For obvious reasons, it's usually easier to see if your baby is a boy. The test, usually given to moms 35 or older, involves inserting a needle into the uterus to remove a small amount of amniotic fluid.
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Sexual differentiation in humans

Medical researchers at Melbourne's Murdoch Children's Research Institute have made a new discovery about how a baby's sex is determined -- it's not just about the X-Y chromosomes, but involves a 'regulator' that increases or decreases the activity of genes which decide if we become male or female. An embryo with two X chromosomes will become a girl, while an embryo with an X-Y combination results in a boy," Ms Croft said. High levels of the SOX9 gene are needed for normal testis development.
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One of the most exciting things about having a child is learning the gender of the baby. Many people choose to find out as soon as possible, while others decide to keep it a surprise. Although you may not see sex organs on a sonogram for weeks, a baby's sex is determined long before it arrives in the world. Gender is determined immediately upon fertilization.
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