Yes, but As of 2025, the chance of error is around 1% when the test is done after the 10th week of pregnancy, according to major medical sources.
You’ve probably seen the ads: a quick blood draw, a few days of waiting, and you’ll know whether to buy pink or blue onesies. Non-invasive prenatal testing (NIPT) for gender has become wildly popular because it’s simple and early. But that simplicity can make people forget one important thing — this is a screening test, not a crystal ball.
The honest answer is: blood gender tests can be wrong, though it’s uncommon. Why it happens, how often, and when you can trust the result is what this article breaks down, using the most reliable evidence available.
What NIPT Actually Measures
NIPT looks for small fragments of cell-free DNA (cfDNA) circulating in your blood. During pregnancy, some of that cfDNA comes from the placenta and contains fetal genetic material. The test reads the number of Y chromosomes present to determine sex.
Because it’s a screening test — not a diagnostic one — it’s designed to flag possibility, not certainty. Major genetics labs explain that NIPT is regarded as a screening test and is remarkably accurate but not perfect. That distinction matters when you’re making decisions based on the result.
The test works best when the so-called fetal fraction (the proportion of fetal cfDNA in your blood) is high enough. If it dips below a certain threshold, the algorithm may struggle to produce a reliable read.
Why We Expect Perfection — And Why It’s Tricky
It’s easy to assume a DNA test is infallible. But biology doesn’t always cooperate. The factors that can throw off a gender blood test are more common than most people realize.
- Testing too early: The most frequent reason for a wrong result. Before 10 weeks, the fetal fraction may be too low to detect Y chromosomes accurately, leading to false negatives (missing a boy) or false positives (detecting a Y chromosome from a vanishing twin or other source).
- Low fetal fraction: If the mother’s body weight or placental function reduces the amount of fetal cfDNA, the test may not have enough genetic material to work with. Some studies link low fetal fraction to higher error rates.
- Maternal fibroids: Uterine fibroids can shed abnormal cell‑free DNA that mimics fetal DNA. Research shows fibroids can cause false‑positive NIPT results because genetic anomalies from fibroid cells get detected as if they came from the fetus.
- Twin and IVF pregnancies: Carrying more than one baby or using donor eggs can introduce extra sources of DNA that complicate the analysis. Contamination risks also rise when multiple embryos are involved.
These scenarios don’t mean the test is unreliable overall — just that a perfect result isn’t guaranteed for every pregnant person. Knowing the possible pitfalls helps set realistic expectations.
What the Numbers Really Show
The strongest evidence on accuracy comes from peer‑reviewed studies and major medical sources. After week 10, the chance that a sex determination from NIPT is incorrect sits around 1 percent. That means for every 100 mothers who test after 10 weeks, roughly 99 get the correct gender read.
But the picture changes when you look at false negatives — tests that incorrectly say female when the baby is male. Some research has found that often underestimated by the way they’re calculated. That doesn’t mean the test is bad; it means the published error rates may be a little optimistic, especially for certain sub‐groups.
Here’s a quick look at how accuracy varies by scenario, based on available research:
| Factor | Impact on Accuracy | Notes |
|---|---|---|
| Test done after 10 weeks | Error rate around 1% | Strong Tier‑1 evidence |
| Test done before 10 weeks | Error rate likely higher | Insufficient fetal DNA is the top cause |
| Low fetal fraction (<4%) | Error rate increased | Test may be reported as “insufficient” rather than wrong |
| Maternal fibroids present | Can cause false positives | Fibroid cfDNA mimics fetal abnormalities |
| Twin or IVF pregnancy | Higher risk of ambiguous result | More sources of cfDNA complicate analysis |
The takeaway: NIPT is very reliable for most pregnancies, but it’s not flawless. The conditions listed above explain most of the errors that do occur.
How to Confirm or Double‑Check the Result
If you’ve had a blood gender test and feel uncertain about the result — maybe it contradicts an earlier ultrasound, or you tested very early — there are straightforward ways to get more certainty.
- Wait for the anatomy scan: Around 18–22 weeks, a skilled sonographer can visualize genital anatomy with high accuracy. This isn’t 100% perfect (umbilical cord position can obscure things), but it’s a widely accepted second check.
- Ask about a repeat NIPT: Some providers will re‑draw blood if the first result was borderline or didn’t meet quality thresholds. A repeat test at 12–14 weeks often improves fetal fraction.
- Understand the test type: Confirm that your NIPT was done by a laboratory that explicitly reports gender accuracy data. Some direct‑to‑consumer kits may have different reliability standards than clinical tests ordered by your OB.
- Consider diagnostic testing if needed: In cases where a sex‑linked genetic condition is suspected, chorionic villus sampling (CVS) or amniocentesis can provide definitive genetic information. These carry a small risk of miscarriage, so they’re not used for casual gender curiosity.
Most families will be satisfied with the combination of NIPT plus anatomy scan. If the two agree, the combined accuracy is very high.
When You Should Still Trust the Blood Test
Despite the caveats above, NIPT remains the most accurate non‑invasive way to determine fetal sex early in pregnancy. The 1‑percent error rate after 10 weeks compares favorably with ultrasound (which can be wrong in 2‑5% of scans, depending on timing and technician experience).
According to NIPT sex determination accuracy data, the test is “remarkably accurate but not perfect.” Most parents who get their gender result from a reputable lab at 10+ weeks can feel confident about it.
Quick reference for common beliefs versus what the evidence says:
| Belief | Evidence |
|---|---|
| “NIPT is 100% accurate” | No test is 100%. The best studies show ~99% after 10 weeks. |
| “If it says boy, it’s definitely a boy” | False positives (Y chromosome detected from maternal source) are less common but warrant evaluation, especially in higher-risk patients. |
| “If it says girl, it might be a hidden boy” | False negatives (missing Y) do occur, especially with low fetal fraction or early testing. |
| “Early tests are just as reliable” | Accuracy improves significantly after week 10; before that, error rates are higher. |
The bottom line is that NIPT is an excellent screening tool, but like any medical test, it has limits. Knowing those limits helps you interpret the result correctly and decide whether additional confirmation is needed.
The Bottom Line
A blood gender test can be wrong, but the odds are in your favor — roughly 99% accuracy after 10 weeks, with errors clustering around early testing, low fetal fraction, or maternal conditions like fibroids. If your result matches later ultrasound findings, you can trust it. If it doesn’t, talk to your OB about repeating the test or waiting for an anatomy scan.
Your obstetrician or midwife can help you weigh the accuracy of your specific NIPT result against your own medical history — including any fibroids or twin pregnancy — so you can feel confident about the next step.
References & Sources
- NIH/PMC. “Nipt False-negative Rates Underestimated” While false positive rates of different NIPT tests may be halfway accurate, reported false-negative rates are most likely too low.
- Thebump. “Ultrasound Wrong Gender” The chance of a sex determination via NIPT being wrong is around 1 percent when the test is conducted after week 10 of pregnancy.