The earliest you can reliably see a baby's gender on ultrasound is generally around 14 to 16 weeks of pregnancy. At this point, the baby's external genitalia have developed enough to make a fairly accurate determination, though accuracy improves closer to 18-22 weeks during the anatomy scan. Before 14 weeks, gender prediction via ultrasound is less reliable and more of a guess. Early attempts around 11-13 weeks using the "nub theory" can give clues but are not as accurate as later scans.

• From about 14 weeks, anatomy begins to show the baby's sex more clearly.
• Most recommendations suggest confirming gender between 16 and 20 weeks for higher accuracy (95-99%).
• The anatomy scan done at 18-22 weeks is the most common and reliable time to determine sex.
• Factors influencing accuracy include baby's position, ultrasound quality, and technician experience.
• Before 14 weeks, ultrasound gender guesses have a lower accuracy rate and can be unreliable.

So, while it's possible to see hints of gender at 11-14 weeks, the best time to confidently see the baby's gender on ultrasound is from 16 weeks onward, with the highest reliability around the standard anatomy scan period between 18 and 22 weeks.