Most parents can find out the sex of their baby between 18 and 20 weeks of pregnancy, during the routine anatomy ultrasound. But if you don’t want to wait that long, blood tests can give you an answer as early as 6 weeks, and some imaging methods become reliable around 14 weeks. The exact timing depends on which method you choose and whether it’s covered by your insurance or available through your provider.
How the Baby’s Body Develops
All embryos start out looking the same. A small structure called the genital tubercle begins forming early on, but it doesn’t start differentiating into distinctly male or female anatomy until around 9 weeks of gestation. By 11 weeks, the structures are beginning to look different, and by 14 weeks the external genitalia are clearly distinguishable. This developmental timeline is why ultrasound-based predictions become more reliable the further along you are.
Blood Tests: As Early as 6 Weeks
The earliest way to learn your baby’s sex is through a blood test that analyzes tiny fragments of fetal DNA circulating in your bloodstream. There are two main options here: at-home commercial tests and clinical screening through your provider.
At-home tests like SneakPeek work by detecting whether Y-chromosome DNA is present in your blood. If it is, the baby is male; if not, female. These tests are available starting at 6 weeks and claim 99.9% accuracy. You collect a small blood sample at home and mail it to a lab, with results typically arriving within a few days. The cost is out of pocket, usually between $80 and $200 depending on how fast you want results.
The clinical version is called NIPT, or noninvasive prenatal testing. Providers typically offer it at 10 weeks or later because the concentration of fetal DNA in your blood is higher by then, which makes results more reliable. NIPT is primarily designed to screen for chromosomal conditions like Down syndrome, but it also identifies fetal sex with high accuracy as part of the same analysis. One recent study tested a newer method at 6 to 9 weeks and correctly identified the sex in all 28 successful cases, though standard practice still starts at 10 weeks. Whether NIPT is covered by insurance often depends on your age and risk factors.
Ultrasound: 14 to 20 Weeks
For most pregnancies, ultrasound is how you’ll find out. The standard anatomy scan happens around 18 to 20 weeks, and it’s part of routine prenatal care in most countries. During this scan, a sonographer examines the baby’s organs, limbs, spine, and brain. If you want to know the sex, they can check the genitalia at the same time.
Research on second-trimester ultrasounds shows they’re extremely accurate. In one study, sonographers were able to determine the sex in 214 out of 215 cases (99.5%), and every one of those predictions turned out to be correct. The single case where they couldn’t make a determination involved a combination of higher maternal BMI, uterine fibroids, and the baby being in an awkward position. So while accuracy is essentially 100% when the sonographer can get a clear view, there are occasional situations where the baby’s position or the mother’s body make it difficult to see.
Some parents get an earlier look during the first-trimester scan, which typically happens between 11 and 13 weeks. At this stage, a skilled sonographer may offer an educated guess, but the external anatomy isn’t fully formed yet. Predictions made after 14 weeks, however, have been shown to be 100% accurate in studies. If you’re hoping for a reliable answer before the 20-week scan, asking at a 14- to 16-week appointment is reasonable.
Diagnostic Procedures: 10 to 16 Weeks
Two procedures that are sometimes performed for medical reasons also reveal fetal sex with near-perfect accuracy. Chorionic villus sampling (CVS) happens between 10 and 13 weeks, and amniocentesis happens around 16 weeks. Both involve collecting a small sample of cells that contain the baby’s full genetic information, so sex determination is about 99% accurate.
These are not routine tests. Providers recommend them when there’s a specific concern about a chromosomal condition or genetic disorder. They carry a small risk of complications, so they wouldn’t be performed solely to find out the baby’s sex. But if you’re having one done for medical reasons, you’ll get that information along with the other results.
What Can Affect Your Results
The reliability of any method depends on timing and circumstances. For blood-based tests, the main variable is how much fetal DNA is circulating in your blood. Earlier in pregnancy, the concentration is lower, which is why NIPT is typically offered at 10 weeks rather than 6 or 7. At-home tests taken very early carry a slightly higher chance of an inconclusive or incorrect result, particularly if the sample is contaminated with outside DNA.
For ultrasound, the most common obstacles are the baby’s position (legs crossed, for example), placental location, higher maternal BMI, and uterine fibroids. All of these can block the sonographer’s view. If the baby isn’t cooperating during your scan, you may be asked to walk around, drink water, or come back for another look. Current clinical guidelines recommend that fetal genitalia be examined as part of the standard second-trimester anatomy review, and that results be shared with the patient if they want the information.
Comparing Your Options at a Glance
- At-home blood test: Available from 6 weeks. Results in days. Out-of-pocket cost. High accuracy but not a medical screening.
- NIPT (clinical blood test): Typically from 10 weeks. Also screens for chromosomal conditions. May be covered by insurance depending on risk factors.
- First-trimester ultrasound: Around 11 to 13 weeks. Sex prediction possible but less reliable before 14 weeks.
- CVS or amniocentesis: Between 10 and 16 weeks depending on the procedure. Nearly 100% accurate but only performed for medical indications.
- Anatomy scan ultrasound: 18 to 20 weeks. Part of standard prenatal care. Essentially 100% accurate when the sonographer gets a clear view.
If you’re eager to know early and willing to pay out of pocket, a blood test at 6 to 10 weeks is your fastest route. If you’re happy to wait for your routine appointments, the anatomy scan around 18 to 20 weeks will give you a definitive answer at no extra cost.