When Can a Baby’s Gender Be Determined? Early and Accurate Methods

When Can a Baby's Gender Be Determined?

One of the most exciting questions for expectant parents is when they can learn the gender of their baby. In modern medicine, gender can be detected at different stages depending on fetal development and the diagnostic methods used. However, contrary to popular belief, a baby's gender is determined long before it is visible on ultrasound.

When Is Gender Genetically Determined?

A baby's gender is determined at the moment of fertilization, based on whether the sperm carries an X or Y chromosome.

• X chromosome → Female (XX)
• Y chromosome → Male (XY)

However, it takes time for external genitalia to develop sufficiently to be identified through imaging.

When Can Gender Be Seen on Ultrasound?

Ultrasound is the most commonly used method. Gender can often be predicted between 13-16 weeks, though accuracy increases later in pregnancy.

11-13 weeks:

Some doctors use the "nub theory" to predict gender, but the error rate is relatively high.

16-18 weeks:

Genital structures become more defined, making gender prediction more accurate if the baby is in a favorable position.

20 weeks (Anatomy scan):

This detailed ultrasound is considered highly accurate and the preferred time for confirming gender.

Therefore, the most reliable period is: 18-22 weeks.

Why Can't Gender Always Be Seen?

Sometimes gender cannot be visualized clearly due to:

• Baby's position
• Closed legs
• Low amniotic fluid
• Maternal obesity
• Poor ultrasound resolution

This does not mean the baby lacks genitalia; it is simply a technical limitation.

When Can Gender Be Determined by Blood Test?

With advances in technology, gender can be identified much earlier than ultrasound.

Non-invasive prenatal testing (NIPT)

By analyzing fetal DNA in the mother's blood, gender can be determined with over 99% accuracy from week 9.

NIPT also screens for chromosomal abnormalities such as Down syndrome.

Other blood tests

Some basic blood tests attempt gender prediction but are less accurate than NIPT.

Which Method Is Most Accurate?

Accuracy rates are generally as follows:

• NIPT: 99%+
• 20-week ultrasound: 95-98%+
• 16-week ultrasound: 80-90%
• 13-week nub theory: 50-80%

The most reliable approach:

• NIPT + 20-week ultrasound

Old Wives' Tales: Scientific or Not?

Many symptoms are believed to predict gender. For example:

• Severe nausea → girl
• Milder symptoms → boy

Research shows that symptoms do not differ based on gender.

Prediction accuracy is essentially: 50%  pure chance.

Chinese Gender Prediction

The Chinese calendar predicts gender based on maternal age and conception month.

It is fun to try, but it has no scientific basis. Accuracy is around: 50%.

For more details, you can check our Chinese Gender Prediction page .

What Is the Best Time to Learn the Gender?

Most accurate timing:

• 18-22 weeks (ultrasound)

For earlier detection:

• 9-week NIPT test

However, blood test results should ideally be confirmed with ultrasound.

In Summary

A baby's gender is determined at conception, but medical tests are needed for confirmation. While blood tests can reveal gender as early as week 9 with high accuracy, ultrasound between 18-22 weeks provides the most reliable visual confirmation. Popular predictions and symptoms are fun but lack scientific validity. Accurate information comes from medical testing and professional evaluation.