You can have a paternity test as early as eight weeks into pregnancy, at the time of birth, or at any point afterward, including when a child is an adult. The timing you choose affects the method used, the cost, and whether the results hold up in court.
During Pregnancy: Three Options
If you want answers before the baby is born, there are three ways to test, each available at a different stage of pregnancy.
Noninvasive Prenatal Paternity Test (After Week 8)
This is the earliest and safest option. Starting at eight weeks of pregnancy, a lab can detect small fragments of fetal DNA circulating in the mother’s bloodstream. The mother gives a standard blood draw, and the potential father provides a cheek swab. The lab then compares the two DNA profiles. There’s no needle going near the uterus, so there’s no risk of miscarriage. For the test to work, the fetal DNA in the mother’s blood needs to reach a minimum concentration, typically between 2% and 4% of the total free-floating DNA in her plasma. Most women hit that threshold by week eight, though factors like body weight can occasionally delay it.
Chorionic Villus Sampling (Weeks 10 to 13)
CVS is an invasive procedure originally designed to screen for genetic conditions like Down syndrome. A provider removes a tiny sample of tissue from the placenta, which shares the baby’s DNA. That sample can also be used for paternity testing. The procedure carries a miscarriage risk of less than 1 in 100. Because the noninvasive blood test is now widely available and carries no physical risk, CVS is rarely chosen solely for paternity purposes.
Amniocentesis (Weeks 14 to 20)
During amniocentesis, a provider uses ultrasound guidance to insert a thin needle through the abdomen and into the uterus, withdrawing a small amount of amniotic fluid. The fluid contains fetal cells with usable DNA. Like CVS, this procedure exists primarily for genetic screening and carries a small miscarriage risk. It’s not a common choice for paternity alone.
At Birth
If you’d rather wait, a paternity test can be done immediately after delivery. The baby’s DNA can come from cord blood collected at the time of birth or from a simple cheek swab taken in the hospital. The potential father provides his own cheek swab. There’s no medical risk at this stage, and collecting samples takes only a few minutes. Some hospitals can coordinate this on-site, while others require you to arrange the test through an outside lab.
After Birth: No Age Limit
A paternity test can be performed on a child of any age, from newborn to adult. The standard method is a painless cheek swab, which collects cells from the inside of the mouth. This works on infants, toddlers, teenagers, and grown adults equally well. There is no medical minimum age for a cheek swab, and no health restrictions for the child or the potential father.
Adults who want to confirm paternity years or even decades later use the same cheek swab process. The DNA doesn’t change over a person’s lifetime, so results are equally reliable whether the child is two days old or forty years old.
Legal Tests vs. At-Home Kits
The timing of your test matters less than how the sample is collected if you need results for a legal purpose. There are two categories of paternity tests, and the distinction comes down to one thing: chain of custody.
A legal paternity test requires that samples be collected by a neutral third party, typically at a lab, clinic, or hospital. Both parties show government-issued identification, and the collector documents every step from swab to sealed envelope. This chain of custody makes the results admissible in court for child support, custody, immigration, or adding a name to a birth certificate.
An at-home test uses the same DNA technology and is just as scientifically accurate, but because you collect the swabs yourself at home, there’s no independent verification of who provided each sample. Courts won’t accept these results. At-home kits are designed for personal knowledge only.
If there’s any chance you’ll need results for a legal matter, start with a legal test. Converting an at-home result into a court-admissible one isn’t possible. You’d need to test again under supervised conditions.
How Accurate the Results Are
Modern DNA paternity tests compare specific genetic markers between the child and the potential father. When the man tested is the biological father, results typically show a probability of paternity of 99.9% or higher. When he is not the biological father, the test excludes him with 100% certainty. These accuracy numbers apply to both prenatal and postnatal testing methods.
False results are extremely rare with accredited labs. The most common source of error isn’t the science but the sample collection, particularly with at-home kits where mix-ups or contamination can occur.
How Long Results Take
Standard cheek swab tests processed through an accredited lab typically return results within three to five business days, though some labs offer expedited options for an additional fee. Prenatal blood-based tests generally take longer, often one to two weeks, because isolating fetal DNA from the mother’s blood is a more complex process. Legal tests may add a day or two due to the additional documentation and verification steps.
Testing When the Father Is Unavailable
If the potential father is deceased or otherwise unable to provide a sample, paternity can still be established through alternative approaches. DNA from the father’s close biological relatives, such as his parents or other children, can be compared to the child’s DNA to determine a biological relationship. Labs can also work with stored biological samples if they exist. The process is more complex and may require a specialized forensic lab, but it remains scientifically viable.