The 20-week ultrasound is an exciting, yet nerve-wracking time for many people.
Most people know it as the scan where they find out the sex of their baby (if they want to know), but the main reason for the scan is to find out if your baby has any underlying problems that require further investigation. For this reason, it is sometimes called an ‘abnormality scan’.
When you’re lying there with Jell-O on your stomach and you see something that resembles a bean hopping around on the screen, it may seem like a miracle that the sonographer can confidently determine your baby’s sex based on what he or she sees—especially when you’re still trying to figure out what’s a leg and what’s a head.
We asked Kate Richardson, Managing Director and Consultant Sonographer at The Birth Company Harley Street and Alderley Edge, part of Portland Hospital, to explain exactly how they do it.
She explains that 12 weeks ago too early to detect any difference in gender on ultrasound. And aAlthough an ultrasound diagnostician may be able to determine the gender as early as 12 weeks, this is not always a given and depends heavily on the doctor’s experience, the quality of the ultrasound equipment, the position of the baby at the time of the examination and the stature of the mother.
Between the 12th and 14th week, the sonographer can obtain a longitudinal ultrasound image and then assess the so-called “fetal nucleus”, which is essentially the baby’s sexual anatomy at this stage.
“For boys, the stud angle is greater than 30 degrees, for girls, it is less than 30 degrees,” says Richardson.
“The quality and position of the image affect the likelihood of determining the correct gender. It may be better to wait until the result is more reliable, although it can be fun to compare your ultrasound images on nub theory websites and guess with your family.”
Out of From the 14th week onwards, your baby is more embryologically developed, explains the ultrasound diagnostician, so that the differences can be seen more clearly.
“Baby girls continue to have a straight bulge that, from the other angle, can look like three white lines between the legs. Baby boys have now developed an appearance that is more consistent with a small scrotum and penis,” she says.
After 20 weeks, she says, an experienced sonographer with high-quality equipment should be able to correctly determine the sex of a baby via ultrasound in over 99% of cases. However, sometimes things don’t go as planned, for example if the baby is in an unfavorable position.
At this stage, a baby girl anatomy rremains as three white lines between the legs on an ultrasound, she explains, and tThe little boy’s scrotum and penis are also more visible to the untrained eye.
