Most pregnant women find out their baby’s sex (if they choose to know) during their mid-pregnancy ultrasound, usually between 16 and 20 weeks. However, the technician may not be able to tell for sure if she can’t get a clear view of the baby’s genitals.
While a baby’s penis or vulva begins forming as early as 6 weeks, boy and girl babies look very similar on ultrasound until about 14 weeks, and it can still be hard to tell them apart for several weeks after that. By 18 weeks, an ultrasound technician should be able to identify the sex if the baby is in a position that allows the genitals to be seen. If not, you may be able to find out the sex if you have another ultrasound later.
Some people find out their baby’s sex through noninvasive prenatal testing (NIPT). This is a blood test that can detect Down syndrome and a few other chromosomal conditions at 10 weeks of pregnancy or later. It also looks for pieces of the male sex chromosome in the expectant mother’s blood to see if she’s carrying a boy or a girl.
Other people find out their baby’s sex from a genetic test like CVS or amniocentesis. These tests are usually used to determine whether a baby has a genetic disorder or a chromosomal abnormality like Down syndromebut may carry a slight risk of miscarriage. CVS is typically done between 10 and 13 weeks and amniocentesis between 16 and 20 weeks.
To see how boys’ and girls’ genitalia develop in the womb, watch our amazing animated video Inside pregnancy: Girl or boy?
Not planning to find out your baby’s sex but curious about your odds of having a daughter or son? See our article on which factors may slightly increase your chances of having boy or girl or check out our Chinese gender predictor.