Baby Gender Test Vs. Ultrasound | What's More Accurate?

By Liz Wood, Health Testing Specialist at at AlphaBiolabs Last reviewed: 09/04/2025

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The only reliable way to find out the sex of a baby before birth is with a DNA test (Baby Gender Test), using a blood sample from the mother.

An ultrasound scan is always going to be less reliable than a DNA test, as the baby’s position and the clarity of the pictures play a part in whether the ultrasound technician can accurately assess the sex of the baby on the day of the scan.

Here, we look at Baby Gender Testing vs Ultrasound scans.

Table of contents

• Ultrasound more reliable after 18 weeks
• Baby gender testing from 6 weeks
• Can a blood test for gender be wrong?
• Can an ultrasound be wrong about gender?
• Can you get conflicting gender results from a baby gender test vs an ultrasound?
• How can I get a baby gender test?

Whether your baby will be a boy or a girl is determined at the time of conception, long before most women even know they are pregnant.

The egg from the mother and the sperm from the father both carry sex chromosomes. The egg always contributes an X chromosome, and the sperm can contribute either an X or a Y chromosome. The sex of the baby is thus determined by the sperm cell that fertilises the egg first. If the sperm is carrying an X chromosome, the baby will be a girl. If the sperm is carrying a Y chromosome, the baby will be a boy.

Despite a baby’s gender being determined when the egg is first fertilised, pregnant women have to wait until their mid-pregnancy scan at around 16 weeks to determine the sex of their baby. However, ultrasound shouldn’t be relied upon. Statistics show that ultrasounds can be wrong up to 10% of the time. That means up to 10 women out of 100 will be told that they’re having a boy or a girl, only to have quite a surprise at the birth!

A quick trawl on the internet shows hundreds of messages from frustrated mothers, complaining about being given the wrong gender prediction at their ultrasound scan.

The fact is that if the technician can’t get a clear view of the baby’s genitals, it may not be possible to tell for sure. The baby may be in a tricky position, the technician may not have sufficient expertise, the scan may have been performed too early, or the image may not be adequately clear. What we need to remember is that ultrasounds are an essential tool for monitoring the healthy progress of a pregnancy, but were not designed for gender prediction.

Ultrasound more reliable after 18 weeks

The statement that gender predictions made by ultrasound have an accuracy rate of around 90% is backed up by Stephen Carr, Professor of Obstetrics & Gynaecology at the Warren Alpert Medical School of Brown University.

Until the 14th week of pregnancy, baby boys and girls look exactly the same on ultrasound. Beyond this point, noticeable anatomical differences in the genitals can show up on the scan. However, mistakes can be made when determining gender because it depends on the clarity of the images and the skills of the person interpreting them, he said.

According to Carr, it is preferable to wait until after 18 weeks of pregnancy to get a more reliable prediction of gender from an ultrasound scan. However, the baby will still need to be in a good position in the mother’s uterus (i.e. not in a breech or feet down position), and the legs will still need to be far enough apart to grant good visibility between them. So, wait until later and hope the baby is in a good position? It’s still not very reassuring, is it?

Order an at-home Baby Gender Test Online

Baby gender testing from 6 weeks

Not only can a blood test be used to scientifically determine the gender of your baby, but it can also be performed at a much earlier stage of your pregnancy – from just 6 weeks.

The AlphaBiolabs At-home Baby Gender Test is a non-invasive DNA test which offers a 99.9% accurate and reliable way of finding out a baby’s gender before birth, with only a blood sample required from the mother.

We are the ONLY UK laboratory to offer the TinyTAP collection device for blood sample collection, allowing you to collect your sample in the comfort of your own home. This convenient, fuss-free method means you can collect your sample with no additional collection fees, and no clinical appointments required, before returning it to our accredited UK laboratory for testing.

Our in-house geneticists then analyse your blood sample for a Y chromosome. As the Y chromosome is male-specific, the detection of a Y chromosome means the baby is a boy. If no Y chromosome is present, the baby is a girl.

The test can also be used in twin pregnancies and will tell you whether at least one foetus is a boy, or that both foetuses are girls.

Our Tiny TAP device offers the ultimate convenience, allowing you to collect your own blood sample at home. However, if you would prefer to have your blood sample collected by one of our specially trained clinicians, you also have the option to order a Clinical Baby Gender Test.

Order your Baby Gender Test now

Can a blood test for gender be wrong?

Our baby gender testing is 99% accurate, making our results extremely reliable.

For the highest chance of a conclusive result, the mother must be at least 6 weeks’ pregnant to ensure that any Y chromosome present in the blood sample is at a detectable level for foetal sex determination.

You can use our Eligibility Calculator to work out if you’re at least 6 weeks pregnant before ordering our Baby Gender Test.

If you are collecting your own sample at home using our TinyTAP device, it is very important that the samples are collected exactly in accordance with the instructions provided in your test kit.

Factors that can affect the results of the test include:

• The level of foetal DNA present in the blood sample at the time of testing – this is highly variable between individuals, and the test cannot determine the level of foetal DNA in the sample, only whether a Y chromosome is present.

• Male DNA contamination – where the DNA sample has become contaminated with male DNA due to handling of the kit contents by a male individual, environmental factors, or other reasons beyond the customer or laboratory’s control.

  Please be assured that, at AlphaBiolabs, every effort is made to minimise the risk of sample contamination throughout the testing process; samples must be collected by females only, following strict collection instructions, and are processed by a female-only lab team.

• A vanishing twin may cause a false result.

Can an ultrasound be wrong about gender?

An ultrasound can be wrong about a baby’s sex.

Although ultrasounds are commonly used to determine the sex of a baby during pregnancy (from 16+ weeks), the results are not always accurate.

Factors such as the baby’s position, movement during the scan, or the clarity of the images can make it difficult for the technician to clearly identify the genital area, which may lead to an incorrect result!

In contrast, a baby gender test using a blood sample – like the one offered by AlphaBiolabs – looks for the presence of the male Y chromosome in the mother’s blood and can be performed much earlier in pregnancy (from 6 weeks).

With an accuracy of 99%, our Baby Gender Test offers a reliable alternative to traditional ultrasound scans for expectant parents who are eager to know the sex of their baby.

Order a Baby Gender Test online now

Can you get conflicting gender results from a baby gender test vs an ultrasound?

It is possible to receive conflicting results from a baby gender test and an ultrasound, but this is usually due to differences in how the tests work and when they are performed.

A DNA-based test, like the AlphaBiolabs Baby Gender Test, analyses foetal DNA found in the mother’s blood to determine the baby’s sex. This method is highly accurate (99%) and can be performed from 6 weeks into pregnancy.

An ultrasound relies on visual interpretation of the baby’s anatomy, usually performed from 16 weeks into pregnancy. Factors like the baby’s position, movement or clarity of the image can make it difficult for the sonographer to clearly see the genital area, increasing the possibility of human error.

Of the two tests, DNA testing offers a more scientifically accurate, reliable result.

Baby gender test vs ultrasound – comparison table

Feature	Baby Gender Test	Ultrasound scan
How it works	Looks for the presence of a Y chromosome in the mother’s blood	Uses sound waves to create images of the baby
Earliest the test can be performed	From 6 weeks into pregnancy	Typically from 16 weeks into pregnancy
Accuracy	99% accurate	Accuracy can vary (typically 95-99%)
Sample collection method	Multiple options for sample collection: Collect your own sample at home using our innovative TinyTAP device Schedule an appointment for a blood draw at one of our walk-in centres Have an AlphaBiolabs sample collector perform your blood draw at a convenient time and location	Conducted by a sonographer using ultrasound equipment
Risk of human error	Extremely low – testing performed at our UKAS 17025-accredited laboratory by expert geneticists	Higher risk – depends on technician and baby’s position on the day of the ultrasound
Convenience	Collect your own blood sample at a time/location that suits you (at home using our TinyTAP device, at one of our walk-in centres or another location)	Requires an in-person appointment at a medical facility
Suitable for early planning	Yes – ideal for gender reveal planning	No – requires waiting until later in pregnancy

How can I get a baby gender test?

Finding out the sex of your baby couldn’t be easier, with our At-home Baby Gender Test.

Simply order your test online and we’ll ship your test kit out to you immediately. Your test kit will contain everything you need to collect your blood sample in the comfort of your own home using our innovative, pain-free TinyTAP device.

Once your sample arrives at our laboratory, testing can begin. Your secure results will be emailed to you the next business day.

Alternatively, you can choose to have your blood sample collected by one of our professional sample collectors* at one of our nationwide walk-in centres or at a time and location convenient to you (via TinyTAP or venous blood draw).

Order your Baby Gender Test online now, call 0333 600 1300 or email [email protected].

*Additional fees apply

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Liz Wood

Health Testing Specialist at at AlphaBiolabs

Liz joined AlphaBiolabs in 2021, where she holds the role of Health Testing Specialist.

As well as overseeing a range of health tests, she is also the lead on several validation projects for the company’s latest health test offerings.

During her time at AlphaBiolabs, Liz has played an active role in the validation of the company’s Genetic Lactose Intolerance Test and Genetic Coeliac Disease Test.

An advocate for preventative healthcare, Liz’s main scientific interests centre around human disease and reproductive health. Her qualifications include a BSc in Biology and an MSc in Biology of Health and Disease.