Baby sex: Some couples choose to find out

Some couples choose to find out their baby 's sex , while others do not. One expert explains what to know either way. Your doctor can use different tests to tell you the sex of your baby starting at around 10 weeks of pregnancy. Often, people find out via a routine ultrasound at 18-20 weeks. A child’s biological sex at birth may not be a 50-50 toss-up, according to a new study from Harvard T.H. Chan School of Public Health. The study, published July 18 in the journal Science Advances, found that birth sex appears to be associated with maternal age, certain genes, and the sexes of older siblings. If you’re wondering when a baby ’s sex develops in the womb, our experts explain the timeline of fetal development —how and when a baby ’s sex can be detected, the best methods to determine it and what factors might affect when parents find out. When and how a baby 's sex develops in the womb Here are the basics.