Can you predict your baby's sex at the nuchal translucency ultrasound?

Often eagerly awaited by parents-to-be, the nuchal translucency ultrasound can sometimes reveal your baby's sex! That said, certain very specific conditions have to be met.

The nuchal translucency ultrasound

Performed between the 11^th and 14^th week of pregnancy, this ultrasound is first and foremost an important medical exam. It is used to assess the risk of certain chromosomal abnormalities, such as trisomy 21.

But for a few years now, another question has been sparking curiosity among parents-to-be during this exam: can you guess the baby's sex at this stage?

The short answer: sometimes, yes, but with caution!

The genital bud

At this early stage, it's important to know that the fetus's genitals are not yet fully formed. Every fetus has a small genital bud, also called the genital tubercle. It's the angle of this bud, relative to the spine, that can give an indication of biological sex:

• Boy: the bud points upward, at an angle greater than roughly 30° relative to the spine.

• Girl: the bud is horizontal or points downward, at an angle of less than 30° relative to the spine.

Here is a diagram to help illustrate it:

Factors that affect accuracy

Even though this method has become very popular on social media and among parents, it's worth remembering that several things can affect how reliable it is:

• The position of the fetus : If the baby is moving, curled up or at an unfavourable angle, it becomes hard to get a good view of the bud. That can skew the reading.
• Ultrasound image quality : The machine's resolution and the clarity of the images are essential to clearly make out the tubercle and measure the angle. Blurry images can lead to misinterpretation.
• Reading the bud correctly takes expertise : An experienced technologist will be better at capturing the right angle and telling anatomical structures apart; it would be a shame to mistake it for part of the umbilical cord!

An unofficial method, but a fun one all the same!

Keep in mind that this method remains unofficial. Accuracy rates vary from one study to another, ranging from 70 to 95%, depending on the week of pregnancy and the technical conditions.

For that reason, many health care professionals point out that predicting sex from the angle of the bud at 12 weeks should be seen above all as a fun moment to share with curious parents-to-be, and not as a medical diagnosis.

Are there more accurate tests or methods?

The most reliable way to find out fetal sex at this stage is still non-invasive prenatal testing using cell-free fetal DNA (NIPT), done with a simple maternal blood draw from the 10th week of pregnancy. It can detect the presence or absence of the Y chromosome (the male chromosome) with over 99% accuracy.

It's also possible, as early as the 7^th week, to determine fetal sex from a blood sample. An option that is just as reliable and safe!

If you don't go with this type of test, sex can be confirmed more reliably at the anatomy scan, done around 20 weeks.

In short, predicting your baby's sex at the nuchal translucency scan is a fun little tradition that fascinates many parents-to-be. But between the angle of the bud, the baby's position, image quality and the technologist's experience, misreadings are always possible. So take the prediction with a grain of salt, keeping in mind that it may well not be final. Either way it will be a lovely surprise, confirmed at 20 weeks or on the day your baby is born!