[Explained by a Doctor] Why Testing Institutions Do Not Perform NIPT After 16 Weeks of Pregnancy

Rewritten on: August 9, 2025

While NIPT can technically be performed after 16 weeks of pregnancy, most facilities limit testing to 16 weeks for medical and ethical reasons, including securing time for confirmatory testing and decision-making, and the restriction under the Maternal Health Protection Act that abortion is limited to under 22 weeks.

Why isn't NIPT recommended after 16 weeks of pregnancy?

Non-invasive prenatal testing (NIPT) is a non-invasive screening test that analyzes fetal-derived cell-free DNA (cfDNA) contained in the mother's blood to check for the possibility of chromosomal abnormalities. Because it can be performed with just a blood draw and carries no risk of miscarriage, it has become increasingly popular among many pregnant women in recent years. However, the testing period is limited to "up to 16 weeks of pregnancy," and many people wonder "why can't it be taken after 16 weeks?"

Even though the test is technically possible, the reason many institutions do not perform NIPT beyond 16 weeks is not simply a matter of operational convenience — there are medical and ethical considerations behind it. Since NIPT is a screening test, a positive result requires a confirmatory diagnostic test (such as amniocentesis), and this is closely related to the fact that Japan's Maternal Health Protection Act limits induced abortion to under 22 weeks of pregnancy. [ref:1]

This article explains, from multiple angles, why NIPT is not offered after 16 weeks of pregnancy — covering test accuracy, clinical judgment, the schedule up to confirmatory testing, and differences with overseas systems. We hope this serves as useful reference material for pregnant women and their partners considering NIPT, helping them decide on the optimal timing for testing.

The relationship between gestational age and NIPT accuracy: cfDNA characteristics and clinical data

The cfDNA analyzed in NIPT is derived from the placenta and is released into the mother's bloodstream when placental chorionic villus cells undergo apoptosis (cell death). It is generally said that a sufficient amount for testing is obtained from around 10 weeks of pregnancy, and while the fetal fraction of cfDNA averages around 10% at 10 weeks, the concentration in the blood rises as gestation progresses. [ref:1]

In other words, test accuracy itself tends to stabilize and even improve as pregnancy progresses, and high accuracy can be maintained through the second and third trimesters. Beyond 20 weeks of pregnancy, the fetal fraction rises further, and detection sensitivity also improves. [ref:6]

In fact, multiple studies targeting women in late pregnancy have reported a positive predictive value of 95% or higher for trisomy 21 (Down syndrome) even after 20 weeks of pregnancy. Multiple clinical studies have also confirmed that detection accuracy for trisomy 18 (Edwards syndrome) and trisomy 13 (Patau syndrome) is maintained or improved as gestational age advances. [ref:2]

Given this, testing should technically be possible after 16 weeks as well, yet it is still not performed in practice. The reason lies not in accuracy but in a more pressing issue: the extremely limited time available for confirmatory diagnosis and decision-making after the test.

Why medical judgment and options become limited

NIPT is ultimately a screening test, and if a positive result is obtained, a confirmatory diagnostic test such as chorionic villus sampling or amniocentesis is required. Since there is also the possibility of a false positive (a case judged positive when no chromosomal abnormality actually exists), confirmatory testing is essential. [ref:7]

Chorionic villus sampling is generally performed around 11 to 14 weeks of pregnancy, and amniocentesis around 15 to 18 weeks. Both tests typically take about 2 to 3 weeks for results to come back.

Furthermore, in Japan, the Maternal Health Protection Act limits induced abortion to under 22 weeks of pregnancy. This is a deadline clearly set by law, and abortion is not permitted after 22 weeks and 0 days of pregnancy under any circumstances. [ref:1]

Therefore, if NIPT is performed after 16 weeks, the time available from confirmatory testing, to result notification, genetic counseling, and finally decision-making by the couple or partners becomes extremely limited, potentially resulting in the loss of practical options. The inability to secure sufficient time for psychological processing and counseling after receiving results places a significant mental burden on pregnant women.

Therefore, the reality is that many facilities "offer testing only during the period when medically and ethically valid decisions can be made." The understanding widely shared in medical settings is that undergoing NIPT is not an end in itself, but a means of making the best choice with sufficient time based on the results. [ref:4]

The schedule and time constraints before NIPT results are finalized

Several steps must be taken between undergoing NIPT and reaching a final decision. The general flow of the schedule is shown below.

1. NIPT blood draw and testing: The blood draw itself is completed on the same day, but it takes about 1 to 2 weeks for the results to come back.
2. Result notification and genetic counseling: If a positive result is obtained, a meeting with a genetic counselor or the attending physician is held.
3. Confirmatory testing (amniocentesis): The amniocentesis is scheduled and performed, and it takes a further 2 to 3 weeks for results to come back.
4. Notification of confirmed results and counseling: Based on the confirmed diagnostic results, the future course of action is discussed with a specialist and genetic counselor.
5. Decision-making by the family: Sufficient time is needed for discussion between the couple or partners.

As shown, at least 4 to 6 weeks should be expected from the NIPT blood draw to the final decision. If NIPT is taken at 16 weeks of pregnancy, the confirmatory test results will come back at the earliest around 20 to 21 weeks, putting the situation right up against the 22-week deadline under the Maternal Health Protection Act. At 17 or 18 weeks, it is highly likely to be too late already — this is the biggest reason why many medical institutions set 16 weeks as the upper limit. [ref:4]

Also, even if the confirmatory test result turns out negative (meaning the NIPT was a false positive), the psychological burden of waiting for the result is immeasurable. Taking the test early has the benefit of shortening this anxious waiting period as much as possible.

How is NIPT handled in late pregnancy overseas?

In some countries overseas, it is possible to undergo NIPT even in late pregnancy. For example, in the UK and parts of the United States, abortion is legally permitted up to around 24 weeks of pregnancy, so in theory NIPT can be performed later and still be acted upon. The UK's NHS (National Health Service) offers NIPT as part of public healthcare, and there are cases where NIPT is performed as an additional test when a conventional maternal serum marker test indicates high risk. [ref:3]

However, in practice, many medical institutions overseas also set the NIPT testing period to early-to-mid pregnancy. The American College of Obstetricians and Gynecologists (ACOG) also recommends that NIPT be performed in early pregnancy, and the view that "earlier is preferable in order to make choices based on the test results" is shared internationally. [ref:8]

The differences between countries' systems are summarized below.

While there are differences between systems, from the standpoint of the effectiveness of decision-making, there is an international consensus that testing should be performed early. In every country, it is widely recognized that in order to make full use of NIPT results, it is essential to secure sufficient time for confirmatory testing and decision-making.

NIPT is a test where "when you take it" matters

NIPT is a test that gives pregnant women an important option, but its value is greatly affected by "when it is taken." Technically, the test can be performed and remains accurate even in late pregnancy. Nevertheless, the reason many institutions do not perform testing after 16 weeks is that there is overwhelmingly insufficient time left for the subsequent confirmatory diagnosis, genetic counseling, and decision-making.

Here is a summary of the key points to keep in mind when undergoing NIPT.

• NIPT can be taken from 10 weeks of pregnancy onward. Early testing is recommended
• If a positive result is obtained, confirmatory testing (such as amniocentesis) takes 2 to 3 weeks
• In Japan, the Maternal Health Protection Act limits abortion to under 22 weeks
• Decision-making after receiving confirmed results also requires a period of psychological preparation
• Technical accuracy is not a problem even after 16 weeks, but time constraints are the biggest hurdle
• An international consensus exists overseas as well that early testing is recommended

In order to make a satisfying decision based on NIPT results, the timing of the test is extremely important. Testing as early as possible should lead to a decision that you and your family will not regret. Once pregnancy is confirmed, we recommend gathering information early and considering scheduling the test.

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Frequently Asked Questions

Q1. Is it absolutely impossible to take NIPT after 16 weeks of pregnancy?

A. Technically, since a sufficient amount of cfDNA (fetal-derived cell-free DNA) exists even in late pregnancy, the test itself can be performed. However, because there is insufficient time to undergo confirmatory testing (amniocentesis) after a positive result and make a decision based on those results, many medical institutions set 16 weeks of pregnancy as the acceptance deadline. Since Japan's Maternal Health Protection Act limits induced abortion to under 22 weeks, there is a high risk of running out of time if testing is done after 16 weeks.

Q2. Does NIPT accuracy decrease as gestational age advances?

A. No, it's actually the opposite. Since the blood concentration of the cfDNA analyzed by NIPT rises as gestational age progresses, test accuracy tends to stabilize or even improve. Some studies have even reported a positive predictive value of 95% or higher for trisomy 21 after 20 weeks of pregnancy. The reason testing is not done after 16 weeks is not an accuracy issue, but mainly the time constraint on confirmatory testing and decision-making. [ref:2]

Q3. If NIPT comes back positive, is it necessary to undergo a confirmatory test?

A. Yes. NIPT is ultimately a screening test (one that checks for possibility) and does not confirm a diagnosis. Since a positive result can include a false positive (a case judged positive when no chromosomal abnormality actually exists), undergoing a confirmatory test such as amniocentesis or chorionic villus sampling is strongly recommended. Making a decision without a confirmatory test cannot be considered medically appropriate.

Q4. Can NIPT be taken in late pregnancy overseas?

A. In some countries, late-pregnancy abortion is legally permitted, so there is some leeway in when NIPT can be performed. For example, in the UK, abortion is permitted up to under 24 weeks of pregnancy. However, many medical institutions overseas also recommend performing NIPT in early to mid pregnancy, and there is an international consensus that "testing should be done early." [ref:3]

Q5. What is the best time to take NIPT?

A. NIPT can be taken from 10 weeks of pregnancy onward, but in order to secure sufficient time for confirmatory testing and decision-making, it is most ideal to take it around 10 to 14 weeks of pregnancy. Testing during this period ensures that, even if a positive result is obtained, you will have time to wait for confirmatory test results (amniocentesis can be performed from 15 weeks onward), receive genetic counseling, and have thorough discussions with your family.

Q6. How long does it take to get NIPT results?

A. NIPT results are typically available about 1 to 2 weeks after the blood draw. However, the time required may vary depending on the testing institution and test items. Additionally, if a positive result is obtained, an additional 2 to 3 weeks are required for confirmatory testing and results, so the overall process should be expected to take at least 4 to 6 weeks. This is another reason why early testing is important.

[References]