how is sex determined in the body growing in uterus of mother?
Answers
Answer:
The UV tests shows a very much clear image of the baby and it is easy for the doctors to determine the sex of baby by the help of these UV photographs.
Explanation:

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PREGNANCY > FETAL HEALTH
Fetal Development: Your Baby’s Sex

by Colleen de Bellefonds
Reviewed on April 18, 2019 

iStock
Learn when and how your baby becomes a boy or girl.
It’s one of the most exciting parts of being pregnant: finding out your baby’s sex. But what, exactly, decides a baby’s sex, and how does it all develop? Here’s your primer to what’s known as fetal sexual differentiation during pregnancy.
Your baby’s genes determine the sex
Your baby’s sex is determined at conception by his or her genes. Embryos with XY chromosomes become boys, and those with XX chromosomes become girls. There are 70 different genes located on the sex chromosomes that define a baby’s sex. Throughout pregnancy, exposure to hormones decided by your baby’s genes affect a baby’s anatomy, physiology and even behavior.
In the beginning, boys and girls are the same
Up until about week 7 to week 8 of pregnancy, both sexes have what’s known as a “genital ridge” — i.e. an identical preliminary set of genitalia that will eventually differentiate to become either male or female sex organs. That means that all 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.
All babies would develop female sex organs if it weren’t for the male hormone testosterone. At around week 7, the Y chromosome signals for the start of testosterone production, and male genitalia begin to develop. Peak concentrations of testosterone in your baby boy’s body are comparable to the amounts found in adult men at around week 16 of pregnancy! Between 16 and 20 weeks, testosterone levels fall until they reach the range found in early puberty by about 24 weeks.