Fetal sex determination can be made at the end of which gestational period?

• A. First trimester
• B. End of 12 weeks
• C. End of 28 weeks
• D. After delivery

Answer: (B)

Timing this concept is about when prenatal methods can reliably reveal a fetus’s sex. By the end of the first trimester, noninvasive prenatal testing using cell-free fetal DNA in the mother’s blood can determine sex. These fetal DNA fragments, including Y chromosome sequences if male, circulate early enough that screening labs can report sex around 12 weeks of gestation. This makes the end of the first trimester the earliest practical window for prenatal sex determination with current testing. Ultrasound gender determination tends to be more reliable later, around the anatomy scan at about 18–20 weeks, and waiting until birth would obviously reveal the sex without prenatal testing.