Baby gender test versus ultrasound

Liz Wood Alphabiolabs

By Liz Wood, Health Testing Specialist at at AlphaBiolabs
Last reviewed: 28/06/2024

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

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 in just 3 working days, or the next day if you upgrade to our Express Service.*

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

*Additional fees apply

Order a baby gender test today

Order your test from an accredited UK laboratory

Liz Wood, AlphaBiolabs

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.

Related articles…

How accurate is a blood test for gender?

In this article, we discuss baby gender testing, how the test works, and the accuracy of a baby gender test.

Read more

Can pregnancy cravings be used to predict baby gender?

In this article, we discuss pregnancy cravings, what they mean, and why DNA testing is the only reliable way to find out the sex of your baby.

Read more

Which parent determines the sex of a baby?

Which parent determines the sex of a baby, and how can you find out the baby’s sex before birth?

Read more