Determining fetal gender can be difficult for a couple of reasons:
- Baby’s position
- Maternal BMI – due to limited image visibility.
When we are determining the gender/sex of the fetus, we will look for characteristic features as signs to determine boy or girl.
For girls there are two signs that we are looking for in both transverse and sagittal sections.
- The hamburger sign is the moniker given to the appearance of the labia and clitoris on an ultrasound. If you look closely at the image, you will see that the labia lips would look similar to a hamburger bun, while the clitoris would resemble the hamburger patty (three echogenic lines)
- The sagittal sign is a bit more complex but involves taking a profile view of the fetus (known as the sagittal plane). We follow the baby’s spine to the tailbone, where we will see a nub at the very end. If there is a downward-pointing notch (called the caudal notch), then the fetus would be a girl. At 16 weeks, the sagittal sign is 90 percent accurate in making the correct determination.
For boys, you would think it would be easier to identify than females, but that’s not always the case. This is especially true before 16 weeks. The determination for male gender would be based on the following signs:
- Male genitalia, including testicles, scrotum, and penis which can be identified at around 15/16 weeks of gestation.
- The sagittal sign in a male fetus differs from a female in that the position of the caudal notch would be upward facing. In a female, the notch would point downward in a 10-degree position. In a male, it would be more in a 30-degree position. If it is somewhere in between, it may be harder to make a definitive determination.
Here at Catch a glimpse, we only perform gender scans after 15/16 weeks gestation to ensure correct gender determination. If we are in doubt, we will send you for a walk or rebook you for a further scan at no extra charge.