Baby's Sex by Ultrasound: When and How Accurate It Is
Reviewed by the LabReadAI medical team
The baby's sex is one of the most exciting questions for parents-to-be. It is most often determined by ultrasound, but accuracy depends on the stage and conditions. Let's break down at what stage the baby's sex is visible on ultrasound, how reliable it is and what can interfere.
At What Stage the Sex Is Visible
In theory differences are visible from 12–14 weeks, but the sex is usually determined reliably at the second screening ultrasound at 18–22 weeks (ultrasound in pregnancy), when the external genitals are well formed. Early on, mistakes are more common.
How Accurate Ultrasound Is for Sex
In the second trimester accuracy is high (usually above 90–95%), but it is not 100%. The result depends on the stage, the baby's position, the amount of fluid, the doctor's experience and the machine. So an early "prediction" is treated as a guess, not a guarantee.
What Can Interfere
- an awkward position of the baby (curled up, legs tucked in);
- an early stage;
- low fluid, the mother's build;
- twins (one baby "hiding").
In such cases the doctor suggests checking the sex at the next ultrasound.
Other Methods: NIPT
The sex is shown more reliably (and earlier) by NIPT — a non-invasive prenatal test on the mother's blood (analysis of fetal DNA), also done to assess chromosomal risks. It determines sex by the sex chromosomes with very high accuracy from 10 weeks, but it is a separate test on indication or by choice.
When to See a Doctor
Determining the sex is a pleasant bonus of ultrasound, not its goal: the main thing is assessing the baby's development and health. The schedule of ultrasounds and screenings — see pregnancy week by week and pregnancy screening.
To understand the ultrasound report in plain language, upload it (PDF or photo) to the imaging and ultrasound interpretation service: the AI will explain the description. This helps you understand the document but does not replace a doctor.
This article is informational. Interpreting ultrasound is the doctor's job.
For informational purposes only
This article is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Please consult a healthcare professional for medical guidance.