The interpretation of the results of an ultrasound to determine gender can sometimes be wrong. A younger gestational age can lead to more inaccurate results.
A research study shows the results of observational studies of ultrasounds performed between 11 and 13 weeks gestational age showed a correct determination of gender in 91.8 percent of cases. However, the accuracy of determination increased with the gestational age: 71.9 percent at 11 weeks, 92 percent at 12 weeks and 98.3 percent at 13 weeks. The study also showed that the determination for males was slightly better than for females, but the results were not statistically significant.