How to Get a DNA Test for an Unborn Baby

Getting a DNA test on an unborn baby usually starts with a simple blood draw from the pregnant person’s arm, typically available from about the tenth week of pregnancy onward. Tiny fragments of fetal DNA circulate in maternal blood, and modern lab techniques can analyze those fragments to screen for chromosomal conditions, determine biological paternity, or even detect certain single-gene disorders. The specific test you need and when you can get it depend on what question you’re trying to answer, and the options range from completely non-invasive screening to diagnostic procedures that involve sampling the placenta or amniotic fluid.

Why a Maternal Blood Draw Works

During pregnancy, the placenta continuously sheds DNA fragments into the pregnant person’s bloodstream. These fragments, called cell-free fetal DNA, come primarily from placental cells undergoing a normal process of cell turnover, though fetal blood cells contribute a small amount as well.¹ The fetal DNA is released into the mother’s blood in tiny pieces wrapped in cell membrane fragments, and it circulates throughout pregnancy. After delivery, this DNA clears out of the bloodstream within minutes, which is strikingly fast compared to how long fetal cells themselves can persist.² That rapid clearance is one reason the test works so cleanly: the DNA you’re measuring is always from the current pregnancy.

By about the seventh week of pregnancy, fetal DNA is detectable in maternal blood, and by the tenth week there’s generally enough of it for reliable analysis. The proportion of cell-free DNA in the mother’s blood that comes from the fetus (called the fetal fraction) matters a lot. If the fetal fraction is too low, the lab may not be able to produce a meaningful result. Most labs set a minimum threshold of around 4% fetal fraction before they’ll report findings.

Non-Invasive Prenatal Testing for Chromosomal Conditions

The most common reason to get a prenatal DNA test is screening for chromosomal conditions like Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). Non-invasive prenatal testing, usually called NIPT or sometimes NIPS, analyzes the cell-free fetal DNA in a maternal blood sample to look for extra or missing chromosomes. It’s a screening test, not a diagnostic one, meaning it tells you the likelihood of a condition rather than giving a definitive yes or no.

That said, the accuracy is remarkably high. A large meta-analysis found that NIPT catches about 99.3% of Down syndrome cases, about 97.4% of Edwards syndrome cases, and about 97.4% of Patau syndrome cases, with false-positive rates below 0.1% for all three.³ Studies of the sequencing methods used in NIPT have reported sensitivities for Down syndrome ranging from about 98.6% up to 100%, with specificities often at or near 100%.⁴

To get NIPT, you typically schedule a blood draw through your OB-GYN, midwife, or a maternal-fetal medicine specialist. Some providers order it routinely at the first prenatal visit after ten weeks; others offer it selectively based on age or risk factors. You don’t need to fast beforehand, and results generally come back within one to two weeks. The test can also determine fetal sex with high accuracy, which some parents want and others prefer to skip.

When You Need a Definitive Answer

Because NIPT is a screen, a positive result doesn’t mean the baby definitely has a chromosomal condition. Confirmatory diagnostic testing requires obtaining actual fetal cells, which means one of two invasive procedures: chorionic villus sampling (CVS) or amniocentesis. CVS involves taking a tiny sample of placental tissue, usually between weeks 11 and 14. Amniocentesis draws a small amount of amniotic fluid, typically performed from around week 15 onward. Both provide enough fetal cells for a full chromosomal analysis, and both are considered the gold standard for diagnosis.

The main concern people have with these procedures is the risk of miscarriage. Older estimates placed the risk at roughly 1 in 100 to 1 in 200, but more recent data paints a more reassuring picture. A systematic review and meta-analysis estimated the procedure-related risk of miscarriage following amniocentesis at about 0.11%, and for CVS at about 0.22%, once you account for the background miscarriage rate that exists regardless of any procedure.⁵ An updated meta-analysis found the procedure-related risk for amniocentesis was about 0.30% overall, but when comparing women with similar risk profiles in the intervention and control groups, the added risk shrank to roughly 0.12% and was not statistically significant.⁶ A cohort study looking specifically at CVS found no statistically significant difference in pregnancy loss between women who had the procedure and a matched control group who did not.⁷

The bottom line on risk is that these procedures are safer than many people assume, though they aren’t zero-risk. If NIPT flags a potential issue, your provider will discuss whether diagnostic testing makes sense for your situation. Some people choose diagnostic testing from the start, especially if they have a family history of a specific genetic condition that NIPT doesn’t cover.

Prenatal Paternity Testing

If the question isn’t about chromosomal conditions but about who the biological father is, non-invasive prenatal paternity testing is an option. It works on the same principle: fetal DNA in the mother’s blood includes genetic markers inherited from the father. By comparing those markers to a DNA sample from the alleged father (collected via cheek swab or blood), a lab can confirm or exclude paternity.

A study using SNP arrays tested 21 pregnant women between 6 and 21 weeks of gestation. Of the 20 samples with sufficient fetal DNA, the test correctly confirmed the biological father in every case, and when each sample was also tested against over 1,800 unrelated men, paternity was correctly excluded 99.95% of the time with zero miscalls.⁸ Another study using forensic-grade sequencing detected paternally inherited fetal DNA markers starting at about 7 weeks of gestation, though earlier samples at 4 weeks showed no detectable fetal fraction.⁹ The strength of the paternity evidence improved as the pregnancy progressed, with more paternally inherited markers becoming detectable at 12 and 20 weeks.

Non-invasive prenatal paternity tests are available through commercial laboratories, and they typically require a blood sample from the mother and a cheek swab from the potential father. Some companies offer “legal” versions that follow strict chain-of-custody protocols so the results can be used in court proceedings, while “peace of mind” versions are cheaper but not admissible as legal evidence. Most providers recommend waiting until at least 7 to 8 weeks of gestation for the best chance of a conclusive result. Research on a newer methodology was able to determine paternity in 63 of 64 early-pregnancy samples (before 7 weeks), though one sample with an extremely low fetal fraction couldn’t be resolved on the first pass.¹⁰

Factors That Can Complicate Results

Several things can affect whether a cell-free DNA test produces a clear result, and body weight is the biggest one. Higher maternal BMI is associated with lower fetal fractions in the blood, which means the test is more likely to come back inconclusive. In one study, obese women had an average fetal fraction of about 9.2% compared to 12.5% in women of normal weight, and the rate of inconclusive results was roughly six times higher in the obese group.¹¹ A larger study found that low fetal fraction occurred in about 4.5% of normal-weight women versus about 20% of obese women, and the rate climbed to over 35% in women with severe obesity.¹² The dilution effect seems to come from the mother’s body shedding more of her own cell-free DNA rather than the fetus producing less. If a first draw comes back inconclusive, your provider may suggest waiting a few weeks and resampling, since fetal fraction generally increases as the pregnancy advances.

Vanishing twin pregnancies, where an early twin stops developing but some of its placental tissue remains, can also cause misleading results. Because the lingering placental tissue can shed DNA with a different chromosomal makeup, it may trigger a false-positive result. One study of false-positive NIPT results found that about 13% of false-positive cases showed evidence of a vanishing twin on ultrasound.¹³ Confined placental mosaicism, where the placenta has a different chromosomal profile than the fetus, accounted for other false-positive and even some false-negative results in that same study.

Maternal age can also shift the numbers. Women aged 35 and older had a higher false-positive rate for trisomy 21 (about 1.5%) compared to women under 35 (about 0.7%) in a large analysis of over 38,000 cases.¹⁴ This is partly because the baseline risk of trisomies rises with age, and the math behind positive predictive values is sensitive to how common the condition is in the population being tested.

Beyond the Big Three Trisomies

NIPT was originally designed to screen for trisomies 21, 18, and 13, but the technology has expanded. Many labs now offer screening for sex chromosome differences (like Turner syndrome or Klinefelter syndrome) and for microdeletion syndromes, which involve small missing pieces of a chromosome rather than whole extra or missing chromosomes.

The most commonly screened microdeletion is 22q11.2 deletion syndrome (also known as DiGeorge syndrome), which can cause heart defects, immune problems, and developmental differences. Detection rates for 22q11.2 deletion have been reported at around 90% to 98% in validation studies, with very low false-positive rates.¹⁵¹⁶ But here’s the catch: because microdeletions are much rarer than trisomy 21, the positive predictive value is far lower. In clinical experience, when women received a high-risk result for 22q11.2 deletion and went on to diagnostic testing, only about 18% of those high-risk calls turned out to be true positives.¹⁷ That means roughly four out of five positive screens for this condition are false alarms. This doesn’t mean the technology is bad; it means that screening for rare conditions inevitably produces more false positives relative to true positives, and anyone getting this screening should understand that a positive result is more of a flag for further testing than an answer.

On a separate front, some labs now offer single-gene non-invasive prenatal testing for conditions like cystic fibrosis, sickle cell disease, and other inherited disorders. When both parents are known carriers, fetal DNA in the mother’s blood can be analyzed to determine whether the baby inherited the disease-causing variant from both parents. One analysis found that a reflex approach using this kind of testing after carrier screening caught about 98.5% of affected pregnancies, compared to only about 41.5% with traditional carrier screening alone.¹⁸ Detection of paternally inherited and new mutations in the fetus is relatively straightforward using current techniques, while detecting maternally inherited variants requires more sophisticated analysis because the mother’s own DNA is the dominant signal in the sample.¹⁹

Insurance and Out-of-Pocket Costs

Whether your insurance covers prenatal DNA testing, and how much you’ll pay out of pocket, depends heavily on your risk category and your specific plan. A review of 19 major U.S. payer policies found that all of them covered cell-free DNA screening for trisomy 21 in women considered high-risk (typically over age 35, or with an abnormal ultrasound or prior affected pregnancy). But coverage for average-risk women was a different story: only 8 of those 19 payers covered NIPT as a first-line screen for trisomy 21 in average-risk pregnancies. Almost none covered routine screening for microdeletions or sex chromosome differences.²⁰

An ironic pattern has emerged in some regions: women on public insurance may have better access to NIPT than those with private plans. A study in Wisconsin found that women with public insurance were more than three times as likely to receive NIPT as an initial screen compared to women with private insurance, because many private plans didn’t cover it for low-risk pregnancies.²¹ Genetic counselors in that study were more likely to discuss financial risks with privately insured patients, suggesting that cost uncertainty steered clinical conversations. Without coverage, NIPT can range from a few hundred to over a thousand dollars, though several commercial labs offer self-pay pricing or financial assistance programs that bring the cost down considerably. Prenatal paternity testing is rarely covered by insurance and typically costs between $1,000 and $2,000 through accredited labs.

The Emotional Weight of Prenatal Testing

Prenatal genetic testing is optional, and decisions about whether to test, what to test for, and what to do with results are deeply personal.²² The psychological research on this is worth knowing before you walk into the blood draw. Women who receive a low-risk (negative) NIPT result tend to experience a measurable drop in pregnancy-related anxiety afterward. But women who receive a high-risk (positive) result experience significant spikes in anxiety, even though the positive result is only a screen that needs confirmation.²³

False-positive results carry a real psychological cost. A systematic review found that false positives on obstetric screening tests lead to an immediate increase in distress, mainly anxiety and stress, for expectant mothers and sometimes fathers. The distress generally faded after confirmatory testing ruled out the condition, but some studies found lingering effects on parent-infant interactions and parental attitudes.²⁴ Given that microdeletion screening has a high false-positive rate relative to true positives, the potential for unnecessary anxiety is real if you opt into expanded panels without understanding what you’re signing up for.

Pre-test counseling is meant to help you think through these scenarios before the results arrive. A genetic counselor can walk you through what each test can and cannot tell you, what follow-up testing might look like, and how you might feel about different outcomes.²⁵ Not every practice has a genetic counselor on staff, but if yours doesn’t, asking for a referral before testing is reasonable and increasingly standard practice.

Cell-Based Testing on the Horizon

The entire field of non-invasive prenatal testing is built on analyzing free-floating fragments of fetal DNA. But a newer approach aims to capture intact fetal cells circulating in the mother’s blood. These cells are extremely rare compared to the DNA fragments, but they carry complete copies of the fetal genome, which opens the door to doing full chromosomal and even whole-genome analysis from a blood draw rather than an invasive procedure.

Researchers have demonstrated microfluidic platforms capable of capturing fetal nucleated red blood cells and placental cells from maternal blood samples.²⁶ The advantage of capturing actual fetal red blood cells, rather than just placental cells, is that fetal blood cells genuinely represent the baby’s genetic makeup. Current NIPT relies on placental DNA, and when the placenta’s chromosomes don’t match the fetus (placental mosaicism), you get discordant results. Capturing fetal cells could sidestep that problem entirely.²⁷

However, higher maternal BMI appears to reduce the yield of circulating fetal cells as well. A study found that in women with normal BMI, about 6% of blood samples produced no fetal cells, compared to roughly 16% in overweight and obese women, and 30% in women with a BMI of 40 or higher.²⁸ Cell-based testing is still largely in the research phase and isn’t widely available as a clinical product, but it represents the direction the field is heading: toward making a blood draw as informative as an amniocentesis, without the needle in the uterus.