Most parents find out their baby’s sex between 18 and 22 weeks of pregnancy, during the routine anatomy scan ultrasound. But depending on which method you choose, you can learn as early as 6 weeks with a consumer blood test, 9 weeks with a clinical blood screen, or 12 to 13 weeks with an early ultrasound. Here’s a breakdown of each option, when it’s available, and how reliable it is.
Consumer Blood Tests: As Early as 6 Weeks
The earliest option available is an at-home blood test, like SneakPeek, which works by detecting tiny fragments of fetal DNA circulating in your bloodstream. If the test picks up Y-chromosome DNA, the baby is male. If none is found, the baby is female. A clinical validation study of 115 completed pregnancies found 100% accuracy at six weeks of gestation, with no false positives and no false negatives. Two samples in the study were inconclusive at that early time point, but none gave a wrong answer.
These tests are not covered by insurance and typically cost between $80 and $200. They’re designed purely for sex determination and don’t screen for genetic conditions. Because the test detects trace amounts of DNA, contamination from handling (for example, if someone male touches the collection kit) can cause a false male result, so following the instructions carefully matters.
NIPT Blood Screening: 9 Weeks
Noninvasive prenatal testing (NIPT) is a clinical blood draw offered through your OB or midwife, and it can determine fetal sex as early as nine weeks. Unlike consumer kits, NIPT’s primary purpose is screening for chromosomal conditions like Down syndrome, but sex identification comes along with those results. The test analyzes the same fetal DNA fragments in your blood, so the mechanism for determining sex is similar to the consumer tests, just bundled with broader genetic screening.
NIPT is widely considered highly accurate for fetal sex. Insurance often covers it when there’s a medical indication, such as advanced maternal age or a prior pregnancy with a chromosomal condition. If you’re already planning to get NIPT for genetic screening, you’ll have the option to learn the sex at the same time, usually around 10 to 12 weeks once results come back.
Early Ultrasound: 12 to 13 Weeks
Some providers attempt to identify fetal sex during a first-trimester ultrasound, typically between 11 and 14 weeks. At this stage, the external genitalia haven’t fully formed yet, so the technique relies on measuring the angle of a small structure called the genital tubercle. If it angles upward more than 30 degrees from the spine, the baby is likely male. If it’s flat or angled downward, the baby is likely female.
The accuracy of this method depends heavily on the week. A study from the Fetal Medicine Foundation tracking 172 pregnancies found the following:
- 11 weeks: Overall accuracy of about 70%. Male fetuses were misidentified as female 56% of the time, while female fetuses were incorrectly called male only 5% of the time.
- 12 weeks: Accuracy jumped to nearly 99%. Males were correctly identified 97% of the time, and females were correct 100% of the time.
- 13 weeks: Accuracy reached 100% for both sexes.
So if your provider offers an opinion at 11 weeks, treat it as a rough guess, especially if they say it’s a girl (since boys at this stage often look female on the scan). By 13 weeks, the prediction is much more dependable. Fetal position matters too. If the baby isn’t in the right position for a clear view of the midsagittal plane, the sonographer simply won’t be able to make a call regardless of the week.
The Anatomy Scan: 18 to 22 Weeks
The anatomy scan, sometimes called the 20-week ultrasound, is the appointment where most parents learn the sex. It’s a routine part of prenatal care, scheduled between 18 and 22 weeks, and its main purpose is checking the baby’s organs, limbs, spine, and overall development. By this point, the external genitalia are fully formed and usually easy to see.
That said, it’s not guaranteed. If the baby’s legs are crossed, if they’re facing away from the ultrasound probe, or if the placenta is in the way, the technician may not get a clear view. In most cases the position cooperates, but some parents leave without an answer and need a follow-up scan. If you want to know the sex, let the sonographer know at the start of the appointment so they can try to get the right angle while they’re scanning.
Genetic Testing: CVS and Amniocentesis
Two diagnostic procedures, chorionic villus sampling (CVS) and amniocentesis, can determine fetal sex with about 99% accuracy because they analyze the baby’s actual chromosomes rather than fragments in your blood. CVS is performed between weeks 10 and 13, and amniocentesis around week 16. Both are invasive procedures that carry a small risk of complications, so they’re reserved for pregnancies where there’s a medical reason to test for genetic conditions. They’re not something you’d pursue just to learn the sex, but if you’re having one done, the sex will be part of the results.
Which Method Makes Sense for You
Your timeline depends on how early you want to know and what testing you’re already planning. If you’re getting NIPT for genetic screening, you’ll likely know by 10 to 12 weeks without any extra cost or effort. If you’re not doing genetic testing and you’re comfortable waiting, the anatomy scan around 20 weeks is the standard, free-with-your-prenatal-care option. Consumer blood tests fill the gap for parents who want to know as early as possible and are willing to pay out of pocket, though they don’t provide any health information about the pregnancy.
For the most reliable ultrasound-based answer before the anatomy scan, 13 weeks appears to be the sweet spot, with studies showing 100% accuracy at that point. Anything earlier than 12 weeks on ultrasound is unreliable enough that most sonographers won’t commit to a prediction.