[Explained by a Doctor] What Happens If You Test Earlier or Later Than the Recommended Testing Window?

Revision date: October 26, 2025

The recommended testing window for NIPT is weeks 10-16 of pregnancy. Testing before week 10 lowers accuracy due to insufficient cffDNA concentration, while testing after week 16 risks leaving insufficient time for confirmatory testing and decision-making. Testing at the right timing is important.

Among expectant mothers considering Non-Invasive Prenatal Testing (NIPT), some may wonder, "Why is the testing window limited to weeks 10 through 16 of pregnancy?" There are various circumstances that might make this a concern—wanting to complete the test before morning sickness symptoms settle down, or realizing pregnancy later and missing the recommended window.

NIPT is a test that non-invasively assesses the risk of chromosomal abnormalities such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13) by analyzing fetal-derived DNA fragments (cell-free fetal DNA: cffDNA) contained in the mother's blood. Compared to conventional definitive tests such as amniocentesis and chorionic villus sampling, it carries no risk of miscarriage and can be performed with just a blood draw, which is why it has spread rapidly in recent years [ref:3].

However, this test also has an optimal timing for administration. Based on medical evidence, this article explains in an easy-to-understand way why the recommended timing for NIPT is set the way it is, and what effects can occur if the test is taken outside that window. We hope that understanding the correct timing for testing will help you feel more at ease when undergoing the test.

The medical basis for why the recommended NIPT window is weeks 10-16 of pregnancy

There are broadly two medical reasons behind why the recommended NIPT window is set at weeks 10-16 of pregnancy. The first is "ensuring sufficient concentration of fetal-derived DNA needed for the test," and the second is "ensuring enough time for confirmatory testing and decision-making after the test."

Fetal-derived DNA fragments (cffDNA) circulate in the mother's blood via the placenta. International research has shown that the concentration of this cffDNA gradually increases as gestational age progresses, reaching the minimum threshold required for testing (about 4%) around week 10 of pregnancy [ref:1]. Meanwhile, week 16, the upper limit of the testing window, is set as a deadline to allow prompt progression to definitive testing and sufficient time for a final decision, should a high-risk result occur.

In this way, the recommended timing for NIPT has been scientifically set based on both "testing accuracy" and "time available for subsequent response," and serves as an important guideline for achieving the best outcome for expectant mothers and their families.

What happens if you test before week 10 of pregnancy?

For NIPT to be performed accurately, the proportion of fetal-derived DNA (cell-free fetal DNA: cffDNA) in maternal blood needs to be at least 4% [ref:1]. In early pregnancy, cffDNA concentration increases with gestational age and meets this threshold from around week 10 of pregnancy onward, and by weeks 11 to 13 of pregnancy, the median fetal DNA concentration has been reported to reach approximately 10% [ref:1].

Before week 9 of pregnancy, cffDNA concentration is often insufficient, making it more likely that no result can be produced and retesting will be required. Testing laboratories check the cffDNA proportion in collected blood samples as a quality control indicator, and if it falls below the threshold, the result may be returned as "indeterminate." In such cases, another blood draw is required, adding to the psychological and financial burden on the expectant mother.

It has also been pointed out that performing the test early may increase the false-negative rate (cases judged negative/"low risk" that in fact have an abnormality) [ref:2]. This is because low cffDNA concentration reduces the test's sensitivity (its ability to correctly identify a positive result when an abnormality is actually present). Specifically, when the cffDNA proportion falls below 4%, faint chromosomal abnormality signals can fall below the detection limit, increasing the risk of a false "normal" result.

Furthermore, in very early pregnancy (weeks 7-8), there is a possibility that a twin pregnancy may be mistakenly identified as a singleton pregnancy, or that results may become complicated due to a vanishing twin (a phenomenon in which one of two fetuses is absorbed early in pregnancy). In such situations, the cffDNA analysis results may not accurately reflect the actual condition of the fetus [ref:4].

Therefore, waiting until week 10 of pregnancy or later maximizes testing accuracy and allows for a reliable result. We fully understand the desire to know the results as soon as possible, but please understand that waiting a few weeks can significantly affect the reliability of the results.

What happens if you test after week 16 of pregnancy?

On the other hand, it is technically possible to undergo NIPT after week 16 of pregnancy. Since cffDNA concentration also increases with gestational age, there is no major issue with the accuracy of results even after week 16. In fact, in terms of cffDNA concentration alone, the DNA proportion is actually higher in later pregnancy.

However, the main reason the recommended NIPT window ends at week 16 relates to the time constraints involved in the response after testing. NIPT is ultimately a screening test, and if a high-risk result is obtained, it is recommended to undergo definitive testing such as amniocentesis or chorionic villus sampling. Performing the definitive test, obtaining the results, and then undergoing subsequent genetic counseling and decision-making can take several weeks.

Therefore, if NIPT is performed after week 16 of pregnancy and a high-risk result is obtained, there is a possibility that the final diagnosis via definitive testing will not be confirmed until after week 20 of pregnancy. As gestational age progresses, the range of subsequent options and scope for medical intervention becomes more limited, so it is important to undergo testing with sufficient time to spare [ref:5].

As a concrete timeline, it typically takes 1-2 weeks for NIPT results to come back, about 1 week to perform the subsequent amniocentesis, and a further 2-3 weeks for the amniocentesis results to come back. In other words, it can take up to about 6 weeks from the NIPT blood draw to the final definitive diagnosis.

Additionally, as pregnancy progresses, attachment to the fetus deepens, which can increase the psychological burden when facing a major decision based on test results. Undergoing testing earlier allows more time to calmly process information and discuss thoroughly with family. It also makes it possible to hold multiple consultations with a genetic counselor or attending physician, making informed decision-making easier to achieve after receiving sufficient information.

The relationship between cffDNA concentration and gestational age

The concentration of fetal-derived DNA (cffDNA) changes in stages as gestational age progresses. The table below summarizes approximate cffDNA concentrations by gestational week and their effect on testing [ref:1].

As this table shows, weeks 10-16 of pregnancy represent the "golden window" that optimizes both "testing accuracy" and "time available for subsequent response." cffDNA concentration is also known to vary depending on the mother's body mass index (BMI); in expectant mothers with a higher BMI, the proportion of maternal-derived DNA relatively increases, which tends to make the cffDNA proportion somewhat lower [ref:4]. Given these individual differences, it is reassuring to undergo testing as early as possible within the recommended window.

The benefits of testing within the recommended window

Undergoing NIPT within the recommended window of weeks 10-16 of pregnancy offers many benefits, including the following.

• The highest level of testing accuracy: Since sufficient cffDNA concentration is secured, results can be obtained with the highest possible sensitivity and specificity. NIPT's sensitivity for trisomy 21 has been reported at over 99% [ref:2].
• Reduced risk of an indeterminate result: Since the cffDNA proportion meets the required threshold, you can avoid the situation of "no result being produced."
• Sufficient time to move on to definitive testing: Even if a high-risk result occurs, there is enough time to undergo amniocentesis or chorionic villus sampling.
• Reduced psychological burden: Learning results early allows sufficient time for genetic counseling and consultation with specialists as needed.
• Time to discuss with family: Time is created to discuss thoroughly with your partner and family based on the test results.
• Optimized pregnancy management: It becomes possible to establish an appropriate pregnancy management plan early, based on the test results.

Points to know before undergoing NIPT

If you are considering undergoing NIPT, we recommend preparing by referring to the following steps.

1. Accurately confirm your gestational age: Confirm your accurate gestational age based on your last menstrual period and ultrasound results. If you are unsure about the calculation of gestational age, please consult your obstetrician.
2. Understand the test in advance: Keep in mind that NIPT is a screening test and not a definitive diagnosis. Bear in mind that if a high-risk result occurs, definitive testing will be necessary.
3. Make use of genetic counseling: Consulting a genetic counselor before testing allows you to obtain accurate information about the meaning of the test, its risks, and how to interpret the results.
4. Have blood drawn at week 10 of pregnancy or later: Visit a testing facility within the recommended window to have blood drawn. Results are typically reported within 1-2 weeks.
5. Next steps based on the results: If the result is low-risk, you can continue your pregnancy with peace of mind. If the result is high-risk, discuss definitive testing and genetic counseling with your attending physician.

Summary

The reason the recommended NIPT window is set at weeks 10 to 16 of pregnancy is based on rational, scientifically grounded reasoning. Before week 10, cffDNA concentration is insufficient and testing accuracy decreases, while after week 16, there is a possibility that insufficient time will remain for the response required after testing [ref:1] [ref:2].

Undergoing testing within the recommended window not only allows you to obtain results with the highest possible accuracy, but also ensures sufficient time to carefully consider your subsequent options. NIPT is a support tool to help expectant mothers and their families spend their pregnancy with peace of mind. Undergoing testing at the appropriate timing helps maximize that value.

If you have any concerns or questions about testing timing, please feel free to consult your obstetrician, a genetic counselor, or the specialist staff at the seeDNA Genetic Medical Research Institute. We provide optimal advice tailored to each expectant mother's individual situation.

／Find out your unborn baby's risk of genetic disease／

Frequently Asked Questions

Q1. From what week of pregnancy can I undergo NIPT?

A. NIPT is recommended to be undergone from week 10 of pregnancy onward. Once week 10 has passed, the concentration of fetal-derived DNA (cffDNA) in maternal blood reaches the minimum level required for testing (about 4%), allowing results to be obtained with high accuracy [ref:1]. Before week 9, concentration is often insufficient, raising the risk of an indeterminate result or a false negative.

Q2. I've passed week 16 of pregnancy—can I still undergo NIPT?

A. Technically, it is possible to undergo NIPT even after week 16 of pregnancy. However, if a high-risk result occurs, performing subsequent definitive testing (such as amniocentesis), obtaining the results, and then completing counseling and decision-making can take several weeks, so there is a possibility that time may run short. Please consult your attending physician or a testing facility as soon as possible.

Q3. What should I do if NIPT returns a "high-risk" result?

A. NIPT is a screening test and not a definitive diagnosis. If a high-risk result occurs, it is recommended to undergo definitive testing such as amniocentesis or chorionic villus sampling. We recommend deciding on your future course of action after thoroughly consulting with a genetic counselor or your attending physician, in conjunction with the results of definitive testing [ref:2].

Q4. How accurate is NIPT?

A. NIPT is said to have a sensitivity of over 99% for trisomy 21 (Down syndrome). Sensitivity for trisomy 18 and trisomy 13 is also high, each over 90%. However, since NIPT is a screening test that determines "the level of risk," and the positive predictive value varies depending on maternal age and the condition being tested for, expert advice is important when interpreting results [ref:2].

Q5. Does a higher body mass index (BMI) affect NIPT results?

A. In expectant mothers with a higher BMI, the proportion of maternal-derived DNA relatively increases, which tends to make cffDNA concentration somewhat lower. As a result, the risk of an indeterminate result (no result obtained) may be slightly elevated. However, within the recommended window (weeks 10-16 of pregnancy), sufficient accuracy can be obtained in most cases [ref:4]. If you have concerns, please consult your physician before testing.

Q6. Can NIPT be performed for twin pregnancies?

A. Yes, NIPT can be performed for twin pregnancies as well. However, analysis can be somewhat more complex compared to singleton pregnancies. In particular, if there is a vanishing twin (a phenomenon in which one of two fetuses is absorbed early in pregnancy), care is needed in interpreting the results. We recommend that those with twin pregnancies confirm details with the testing facility in advance.

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