NIPT false positives: Understanding confined placental mosaicism

Quick take: A false‑positive NIPT result can arise when the placenta, not the baby, carries a chromosomal mix—a condition called confined placental mosaicism (CPM). CPM means the cell‑free DNA circulating in your blood reflects placental, not fetal, genetics, so the test may flag an abnormality that isn’t actually present in the baby. Your next step is usually a diagnostic procedure (like CVS or amniocentesis) and a detailed ultrasound to confirm the true status of the fetus. While CPM can feel alarming, most cases resolve with reassuring follow-up testing and result in healthy babies.

It’s 2 a.m., you’ve just finished a restless night of nausea, and the screen on your phone lights up with a headline: “Your NIPT shows trisomy 21.” Your heart skips a beat. You scroll, read, and wonder whether the result means you’ll be raising a child with Down syndrome—or whether there’s another explanation you haven’t heard of yet. The uncertainty can feel overwhelming, especially when you’re already navigating the physical and emotional rollercoaster of pregnancy.

We hear this story a lot: a hopeful parent receiving an unexpected positive screen, feeling a wave of panic, then learning that the placenta’s DNA, not the baby’s, caused the alarm. The good news is that many of these “false‑positive” screens turn out to be harmless, and understanding why can calm the anxiety while you plan the right follow‑up care. In this article, we’ll walk you through what confined placental mosaicism (CPM) is, why it can make a non‑invasive prenatal test (NIPT) appear abnormal, and what it means for your pregnancy journey.

We’ll explain the science behind CPM in plain language, explore how common it is, and outline the steps your healthcare provider may recommend next. You’ll also find practical guidance on discussing results with your care team, understanding the emotional impact, and even how to monitor your pregnancy if CPM is confirmed. Our goal is to give you the knowledge and confidence to navigate this moment with clarity and calm.

What is confined placental mosaicism and how does it affect NIPT results?

Confined placental mosaicism (CPM) is a condition in which two or more genetically distinct cell lines are present in the placenta, while the fetus itself has a single, uniform karyotype. In simpler terms, some placental cells carry a different number of chromosomes than the baby’s cells. Because NIPT analyzes cell‑free DNA (cfDNA) that originates primarily from the placenta, the test can pick up the abnormal chromosome count from the placental cells and report a positive result, even if the fetus’s chromosomes are completely normal.

To understand CPM, it helps to visualize the placenta as a dynamic organ with its own genetic blueprint. During early pregnancy, the trophoblast—the outer layer of the developing embryo that becomes the placenta—shears tiny fragments of its DNA into the maternal bloodstream. These fragments are what NIPT sequences to screen for chromosomal conditions like Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). When CPM is present, the placenta contains a mix of normal and abnormal cells, and the cfDNA released into your bloodstream reflects this mosaic pattern. The NIPT algorithm, which is designed to detect even small imbalances in chromosome counts, may then flag a potential abnormality based on the placental DNA, not the baby’s.

CPM can involve any chromosome, but it most often affects chromosomes 13, 18, 21, and the sex chromosomes—precisely the same chromosomes that NIPT is designed to screen for. The degree of mosaicism (the percentage of placental cells that carry the extra chromosome) can vary widely, ranging from a tiny patch to a majority of placental tissue. The higher the proportion of abnormal cells, the more likely the NIPT will register a positive result. For example, if 30% of the placental cells carry an extra chromosome 21, the cfDNA in your bloodstream may show a higher-than-expected proportion of chromosome 21 material, triggering a "high risk" result for trisomy 21.

It’s also worth noting that CPM can occur in different layers of the placenta. The placenta develops from two distinct cell layers: the cytotrophoblast (the outer layer that interfaces with your bloodstream) and the mesenchymal core (the inner layer that supports the placenta’s structure). CPM can be confined to either layer or both, and the location of the mosaicism can influence how it affects NIPT results. For instance, if the mosaicism is limited to the mesenchymal core, it may not shed as much cfDNA into your bloodstream, making it less likely to trigger a false positive. On the other hand, mosaicism in the cytotrophoblast is more likely to be detected by NIPT because this layer releases cfDNA directly into your circulation.

How does CPM cause a false‑positive NIPT result?

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1. Unequal contribution of placental cfDNA. The placenta sheds cfDNA in proportion to its surface area and activity. If a sizable region of the placenta carries an extra chromosome, that region will release more of that chromosome’s DNA into the maternal circulation, skewing the overall cfDNA ratio. For example, if a large patch of placental tissue has trisomy 21, the cfDNA in your bloodstream will contain a higher proportion of chromosome 21 material, making the NIPT algorithm more likely to flag a potential abnormality.
2. Sampling bias. NIPT draws a relatively small blood sample at a single point in time. If the sampled cfDNA comes disproportionately from a mosaic area, the test may over‑estimate the chromosomal dosage. This is why some women receive different NIPT results when retested—if the second blood draw captures cfDNA from a different placental region, the proportions of chromosomal material may shift.
3. Technical sensitivity. Modern NIPT platforms are extremely sensitive; they can detect even low‑level mosaicism that would be invisible on a standard ultrasound. This sensitivity is a strength for true fetal aneuploidy detection, but it also means the test can flag placental abnormalities that do not affect the baby. For instance, some NIPT assays can detect mosaicism levels as low as 10–20% in the placenta, which may not have any clinical significance for the fetus.

Because NIPT does not differentiate between placental and fetal DNA, the result is reported as a “screen‑positive” for the chromosome in question. The laboratory report may include a comment such as “Possible confined placental mosaicism” if the algorithm detects an atypical cfDNA pattern, but many labs simply state “high risk” without further explanation. This lack of clarity can add to the confusion and anxiety for expectant parents, which is why follow-up testing and counseling are so important.

It’s also helpful to understand that NIPT results are often reported as a "risk score" rather than a definitive diagnosis. For example, a result might read "1 in 100 risk for trisomy 21," meaning that based on the cfDNA proportions, your pregnancy has a 1% chance of the baby having Down syndrome. When CPM is present, this risk score is artificially inflated because the cfDNA reflects the placental mosaicism rather than the fetal chromosomes. This is why diagnostic testing, such as CVS or amniocentesis, is necessary to confirm the true status of the fetus.

How common is CPM and who is more likely to have it?

CPM is not rare. Population studies estimate that about 1–2% of pregnancies have some form of placental mosaicism, and up to 0.5% can lead to a detectable NIPT false‑positive result. The prevalence varies by chromosome; for example, CPM involving chromosome 21 occurs in roughly 0.2% of pregnancies, while CPM of chromosome 13 or 18 is slightly less common. These numbers may seem small, but when you consider that millions of women undergo NIPT each year, CPM is a relatively frequent cause of false-positive results.

Several risk factors have been associated with a higher chance of CPM:

• Maternal age. Advanced maternal age (≥35 years) is linked to an overall increase in chromosomal abnormalities, including CPM, though the effect size is modest compared with true fetal aneuploidy. This is because older eggs are more prone to errors during cell division, which can lead to mosaicism in the placenta.
• Assisted reproductive technologies (ART). IVF and other ART procedures may alter early placental development, modestly raising CPM risk. The exact mechanism isn’t fully understood, but it may be related to the hormonal environment during embryo culture or the manipulation of embryos during the IVF process.
• Placental pathology. Conditions such as placental infarcts (areas of dead tissue), velamentous cord insertion (where the umbilical cord attaches to the edge of the placenta), or early‑onset growth restriction have been observed more frequently in CPM cases. These conditions can disrupt the normal development of the placenta, increasing the likelihood of mosaicism.
• Previous miscarriage. Women with a history of early pregnancy loss sometimes have higher rates of placental mosaicism, though the relationship is still under study. It’s thought that some miscarriages may be caused by undetected CPM, which can lead to placental insufficiency and pregnancy loss.

It’s important to remember that CPM can occur in any pregnancy, regardless of age or health, and most women who experience it will have a completely healthy baby. The presence of CPM doesn’t mean there’s anything "wrong" with your pregnancy—it’s simply a biological quirk that can occasionally confuse screening tests. If your NIPT result comes back positive, your provider will likely recommend additional testing to determine whether CPM is the cause.

One factor that *doesn’t* increase the risk of CPM is maternal lifestyle or behavior. Unlike some pregnancy complications, CPM isn’t linked to diet, exercise, stress, or environmental exposures. It’s a random event that occurs during the early stages of placental development, and there’s nothing you could have done to prevent it. This can be reassuring to hear when you’re feeling overwhelmed by a positive NIPT result.

Distinguishing CPM from true fetal mosaicism and other chromosomal anomalies

True fetal mosaicism means that the fetus itself contains two or more cell lines with different chromosome numbers. This condition can affect development, depending on the proportion of abnormal cells and which chromosomes are involved. In contrast, CPM is limited to the placenta and does not inherently alter fetal genetics. However, the two conditions can sometimes overlap, making it challenging to distinguish between them without diagnostic testing.

Clinicians use a combination of ultrasound findings, biochemical markers, and diagnostic testing to differentiate CPM from true fetal mosaicism or other chromosomal anomalies. Here’s a closer look at how these tools work together:

When a screen‑positive NIPT result is obtained, the first step is often a detailed ultrasound to assess fetal growth, anatomy, and placental appearance. A normal ultrasound can be reassuring, as it suggests that the fetus is developing typically and that the positive NIPT result may be due to CPM. However, some structural anomalies or growth restrictions may hint at true fetal mosaicism or aneuploidy, which would prompt further diagnostic testing.

If the ultrasound is reassuring, the provider may recommend a diagnostic test—usually chorionic villus sampling (CVS) because it samples placental tissue directly, which can confirm CPM. CVS is typically performed between 10 and 13 weeks of pregnancy and involves taking a small sample of placental tissue through the cervix or abdomen. If the CVS result shows the same abnormality flagged by NIPT, CPM is confirmed. However, CVS also carries a small risk of miscarriage (about 0.1–0.3%), so many clinicians prefer amniocentesis (sampling amniotic fluid) as the next step to evaluate fetal cells directly.

Amniocentesis is usually performed after 15 weeks of pregnancy and involves inserting a thin needle into the amniotic sac to collect a small amount of fluid. The cells in this fluid are fetal in origin, so a normal amniocentesis result alongside an abnormal CVS result strongly supports CPM. However, if the amniocentesis also shows an abnormality, it suggests true fetal mosaicism or aneuploidy, which may require additional counseling and management.

In some cases, providers may recommend both CVS and amniocentesis to get a complete picture of the placental and fetal genetics. This approach can be particularly helpful when the ultrasound shows concerning findings or when the NIPT result is ambiguous. For example, if the CVS shows mosaicism but the amniocentesis is normal, it’s likely that the mosaicism is confined to the placenta. On the other hand, if both tests show the same abnormality, it suggests that the fetus is affected.

What follow‑up tests are recommended after a CPM‑related false positive?

Once a false‑positive NIPT result is suspected, a structured follow‑up plan helps clarify the true fetal status while minimizing anxiety. The goal is to confirm whether the abnormality is confined to the placenta or also present in the fetus, so you and your provider can make informed decisions about your pregnancy. Here’s a step-by-step look at the follow-up process:

• Targeted ultrasound. A high‑resolution scan (often called a “level II” or “anomaly scan”) at 18–22 weeks evaluates fetal anatomy, measures growth parameters, and looks for placental abnormalities such as calcifications or uneven thickness that can hint at CPM. This ultrasound is more detailed than a standard scan and can detect subtle signs of fetal anomalies or growth restriction. If the ultrasound is normal, it’s a strong indicator that the NIPT result may be a false positive due to CPM.
• Chorionic villus sampling (CVS). Performed between 10–13 weeks, CVS retrieves placental tissue. If the CVS result shows the same abnormality flagged by NIPT, CPM is confirmed. If CVS is normal, the NIPT result is likely a false positive, and the fetus is presumed chromosomally normal. CVS is particularly useful for confirming CPM because it directly samples the placenta, but it’s important to discuss the small risk of miscarriage with your provider.
• Amniocentesis. Typically done after 15 weeks, this test samples fetal cells from the amniotic fluid. A normal amniocentesis result alongside an abnormal CVS result strongly supports CPM. Amniocentesis is often preferred over CVS for follow-up because it directly assesses the fetal chromosomes, but it’s performed later in pregnancy, which can add to the waiting period.
• Non‑invasive follow‑up. Some labs offer repeat NIPT or a different platform (e.g., whole‑genome sequencing‑based NIPT) to reassess cfDNA ratios. While this can provide additional data, it does not replace a diagnostic test. Repeat NIPT may be helpful if the initial result was borderline or if there were technical issues with the first test, but it’s not a substitute for CVS or amniocentesis.
• Maternal serum screening. Combined first‑trimester screening (nuchal translucency + PAPP‑A + β‑hCG) can provide complementary risk information, though its utility after a positive NIPT is limited. This screening is less specific than NIPT but can offer additional context, especially if the NIPT result is ambiguous.

Because each test has its own risk‑benefit profile, your provider will tailor the pathway to your gestational age, personal preferences, and the specific chromosome involved. For many families, the combination of a reassuring ultrasound and a normal amniocentesis is enough to clear the concern. However, if CPM is confirmed, your provider may recommend additional monitoring to ensure the placenta is functioning properly and the baby is growing as expected.

If you’re curious about how the numbers stack up for your own case, you can explore the NIPT / cfDNA Interpreter to see how different percentages of placental mosaicism might influence the reported risk. This tool can help you understand the relationship between the cfDNA proportions in your bloodstream and the likelihood of CPM or true fetal abnormalities.

Potential impact of CPM on pregnancy outcomes and neonatal health

Most pregnancies affected by CPM result in healthy infants. However, several studies have identified modest associations between CPM and certain obstetric complications. Understanding these potential impacts can help you and your provider monitor your pregnancy more effectively and address any concerns that arise.

• Intrauterine growth restriction (IUGR). Because the placenta may be functionally compromised, some CPM cases show slowed fetal growth, especially when the abnormal cell line makes up a large portion of the placental tissue. IUGR occurs when the baby is smaller than expected for their gestational age, which can sometimes lead to complications like preterm birth or low birth weight. If CPM is confirmed, your provider may recommend more frequent ultrasounds to monitor the baby’s growth and ensure the placenta is functioning properly.
• Pre‑eclampsia. There is a slightly higher incidence of hypertensive disorders in pregnancies with CPM, possibly linked to abnormal placental vasculature. Pre-eclampsia is a serious condition characterized by high blood pressure and organ damage, and it can affect both the mother and baby. If you develop symptoms like severe headaches, vision changes, or sudden swelling, it’s important to contact your provider immediately.
• Preterm birth. A minority of CPM pregnancies deliver before 37 weeks, often related to the same placental insufficiency that drives IUGR. Preterm birth can increase the risk of complications for the baby, such as breathing difficulties or developmental delays, so your provider may recommend additional monitoring or interventions to reduce this risk.

Importantly, these risks are not absolute, and most women with CPM have uncomplicated pregnancies. Neonatal outcomes are generally excellent when the fetus’s karyotype is normal. In rare cases where CPM involves a chromosome that also causes a fetal syndrome (e.g., trisomy 21), the baby can be affected if some fetal cells also carry the abnormality—a scenario called “true fetal mosaicism.” This is why diagnostic testing is so important: it helps distinguish between CPM and true fetal mosaicism, which have very different implications for the baby’s health.

If CPM is confirmed, your provider may recommend additional monitoring during pregnancy to ensure the placenta is functioning properly. This could include more frequent ultrasounds to check the baby’s growth, non-stress tests to monitor the baby’s heart rate, or Doppler studies to assess blood flow in the placenta and umbilical cord. These tests are non-invasive and can provide valuable reassurance as your pregnancy progresses.

It’s also worth noting that CPM doesn’t affect the baby’s long-term development. Once the baby is born, the placenta is no longer needed, and any mosaicism confined to the placenta won’t have any lasting impact on the child’s health. Most babies born after a CPM diagnosis grow and develop normally, with no increased risk of developmental delays or other health issues.

How CPM is detected during pregnancy: Signs and diagnostic clues

CPM is often discovered incidentally during follow-up testing after a positive NIPT result, but there are some subtle signs and diagnostic clues that can hint at its presence earlier in pregnancy. Understanding these clues can help you and your provider interpret your test results more accurately and plan the appropriate next steps.

One of the earliest signs of CPM can be an abnormal NIPT result that doesn’t align with other screening tests or ultrasound findings. For example, if your NIPT shows a high risk for trisomy 21 but your first-trimester combined screening (nuchal translucency + blood tests) is low risk, it may suggest that the NIPT result is due to CPM rather than a true fetal abnormality. Similarly, if your NIPT result is positive but your ultrasound at 12–14 weeks shows no structural anomalies or markers for aneuploidy, CPM becomes a more likely explanation.

Another clue can come from the cfDNA proportions reported by the NIPT lab. Some labs provide a quantitative measure of the cfDNA signal, such as the "chromosome proportion" or "z-score." If this proportion is only slightly elevated (e.g., just above the threshold for a positive result), it may suggest low-level mosaicism in the placenta, which is more likely to be CPM. On the other hand, a very high proportion may indicate true fetal aneuploidy or high-level mosaicism, which would prompt more urgent follow-up.

During a detailed ultrasound, your provider may look for subtle signs of placental dysfunction that can be associated with CPM. These signs can include:

• Placental calcifications. Small white spots on the placenta that can indicate areas of dead or dying tissue. While calcifications are common in later pregnancy, they can sometimes be an early sign of placental mosaicism.
• Uneven placental thickness. A placenta that appears thicker or thinner in certain areas may suggest mosaicism, as different cell lines can affect the placenta’s structure and function.
• Velamentous cord insertion. This occurs when the umbilical cord attaches to the edge of the placenta rather than the center. While it’s not specific to CPM, it’s sometimes seen in pregnancies with placental mosaicism.
• Reduced fetal growth. If the baby is measuring smaller than expected for their gestational age, it may be a sign of placental insufficiency, which can occur with CPM.

If CPM is suspected based on these clues, your provider may recommend diagnostic testing to confirm the diagnosis. As mentioned earlier, CVS is often the first step because it directly samples the placenta. If the CVS result shows mosaicism, your provider may then recommend amniocentesis to check the fetal chromosomes. In some cases, they may also suggest a placental biopsy after delivery to confirm the diagnosis and provide additional information for future pregnancies.

It’s important to note that not all cases of CPM show these signs, and many are only discovered after a positive NIPT result. If your provider suspects CPM, they’ll likely recommend a combination of ultrasound and diagnostic testing to get a complete picture of your pregnancy’s health.

Emotional and psychological impact of a false-positive NIPT result

Receiving a positive NIPT result can be an emotionally overwhelming experience, even if you’re later reassured that it was a false positive due to CPM. The uncertainty, fear, and waiting period between the initial result and follow-up testing can take a toll on your mental health and well-being. It’s completely normal to feel a range of emotions during this time, from anxiety and sadness to frustration and even guilt. Understanding these feelings and knowing how to cope can help you navigate this challenging period.

One of the most common emotions parents experience after a positive NIPT result is anxiety. The sudden shift from expecting a healthy pregnancy to facing the possibility of a chromosomal abnormality can be jarring. You might find yourself constantly worrying about the baby’s health, replaying the result in your mind, or feeling on edge during the waiting period for follow-up tests. This anxiety can be compounded by the lack of immediate answers—NIPT is a screening test, not a diagnostic one, so you may feel stuck in limbo until you receive the results of CVS or amniocentesis.

It’s also common to feel a sense of grief or loss, even if the result turns out to be a false positive. The idea of a "perfect" pregnancy can feel shattered, and you might mourn the loss of the carefree experience you imagined. These feelings are valid, and it’s okay to acknowledge them. Many parents find it helpful to talk about their emotions with their partner, a trusted friend, or a mental health professional. You don’t have to go through this alone, and reaching out for support can make a big difference.

Another challenge is the feeling of isolation. Pregnancy is often portrayed as a joyful, exciting time, and it can be hard to share your worries with others when you feel like you’re supposed to be happy. You might worry about burdening your partner or family with your fears, or you might feel like no one understands what you’re going through. Connecting with other parents who’ve had similar experiences—whether through online support groups, forums, or local networks—can help you feel less alone. Hearing their stories and learning how they coped can provide comfort and perspective.

During this time, it’s important to be kind to yourself. Give yourself permission to feel whatever emotions come up, without judgment. Practice self-care by prioritizing rest, eating nourishing foods, and engaging in activities that bring you comfort, whether that’s reading, walking, or spending time with loved ones. Mindfulness techniques, such as deep breathing or meditation, can also help calm your mind and reduce anxiety. If your feelings become overwhelming, don’t hesitate to seek professional support from a therapist or counselor who specializes in perinatal mental health.

Your healthcare provider can also be a valuable source of support. Many obstetricians and midwives are experienced in helping parents navigate the emotional impact of a positive NIPT result, and they can connect you with resources like genetic counselors or support groups. Genetic counselors, in particular, are trained to provide emotional support alongside medical information, and they can help you process your feelings while making decisions about follow-up testing.

Remember that it’s okay to ask questions and advocate for yourself during this process. If you’re feeling confused or overwhelmed by your test results, don’t hesitate to ask your provider to explain things in a way that makes sense to you. You might also find it helpful to write down your questions ahead of time so you don’t forget anything during your appointments. The more informed you are, the more empowered you’ll feel to make decisions about your care.

Finally, try to focus on the present moment. It’s easy to get caught up in "what ifs" and worst-case scenarios, but dwelling on these thoughts can amplify your anxiety. Instead, remind yourself that most false-positive NIPT results are due to CPM and that the vast majority of these pregnancies result in healthy babies. While the waiting period can feel endless, each day brings you closer to the answers you need—and to the joy of meeting your little one.

Limitations of NIPT technology in detecting CPM and how labs report findings

NIPT is a powerful screening tool, but it’s important to understand its limitations, especially when it comes to detecting confined placental mosaicism (CPM). Because NIPT relies on cell-free DNA (cfDNA) from the placenta, it can’t distinguish between placental and fetal DNA, which means it can’t directly identify CPM. Instead, CPM is often inferred when follow-up diagnostic testing (like CVS or amniocentesis) reveals a discrepancy between the placental and fetal chromosomes. Here’s a closer look at the key limitations of NIPT and how labs report findings related to CPM:

• Inability to separate placental from fetal DNA. Current NIPT platforms analyze all cfDNA in the maternal bloodstream, which is a mix of maternal, placental, and (to a lesser extent) fetal DNA. Because the placenta is the primary source of cfDNA, any mosaicism in the placenta will be reflected in the NIPT result. This means that even if the fetus is chromosomally normal, the test may still flag an abnormality if the placenta contains mosaic cells. This limitation is inherent to the technology and isn’t something that can be "fixed" with more advanced testing—it’s simply how NIPT works.
• Variable fetal fraction. The proportion of fetal (placental) cfDNA in maternal blood typically ranges from 4% to 20%. A low fetal fraction can make it harder for NIPT to detect true fetal abnormalities, while a high fetal fraction can amplify the signal from placental mosaicism, increasing the chance of a false-positive result. For example, if your fetal fraction is on the higher end (e.g., 15–20%), the NIPT may be more likely to pick up low-level mosaicism in the placenta, even if it’s not clinically significant. Some labs will report the fetal fraction alongside your NIPT results, which can provide additional context for interpreting the findings.
• Reporting conventions. Many laboratories include a disclaimer in their NIPT reports, such as “Results reflect placental DNA; discordant results may occur.” This is a way of acknowledging that the test is screening placental DNA, not fetal DNA, and that false positives (or false negatives) are possible. However, not all labs provide this level of detail. Some may simply report a "high risk" or "low risk" result without explaining the potential for CPM. This can make it harder for parents to understand why their NIPT result might not match the outcome of follow-up testing.
• Detection threshold. Most NIPT assays are calibrated to detect mosaicism levels of 20% or higher in the placenta. This means that if the mosaicism is present in less than 20% of placental cells, the NIPT may not flag it, leading to a false-negative result. Conversely, if the mosaicism is present in a higher proportion of cells, the NIPT may report a false-positive result. The detection threshold varies by lab and by the specific NIPT platform, so it’s worth asking your provider or the lab for details about how their test is calibrated.

Because of these constraints, clinicians counsel patients that a positive NIPT result is a “high-risk” finding that warrants diagnostic confirmation, not a definitive diagnosis. The report’s language, combined with your clinical picture (such as ultrasound findings), guides the next steps. For example, if your NIPT shows a high risk for trisomy 21 but your ultrasound is normal, your provider may suspect CPM and recommend CVS or amniocentesis to confirm the diagnosis.

It’s also worth noting that NIPT technology is constantly evolving. Some newer platforms use whole-genome sequencing or other advanced techniques to improve accuracy and reduce the risk of false positives. However, even these advanced tests can’t completely eliminate the possibility of CPM-related false positives, so diagnostic testing remains the gold standard for confirming or ruling out chromosomal abnormalities.

Counselling guidance for clinicians and patients on interpreting CPM‑related results

Effective communication helps reduce anxiety and supports informed decision‑making. Here are key points clinicians can share with patients to help them understand and navigate CPM-related results:

• Clarify the meaning of “screen‑positive.” Emphasize that NIPT screens for chromosomal risk but does not diagnose; a positive result could stem from CPM, true fetal mosaicism, or a genuine aneuploidy. Use plain language to explain that the test is looking at placental DNA, not the baby’s DNA, and that this is why false positives can occur. For example, you might say, “The test is like a smoke detector—it can alert us to a potential problem, but it doesn’t tell us exactly what’s causing the alarm.”
• Discuss the prevalence and outcomes. Explain that CPM is relatively common and most often results in a healthy baby, though a small increase in growth‑related complications exists. Share statistics to provide context, such as “About 1–2% of pregnancies have some form of placental mosaicism, and most of these babies are born healthy.” This can help reassure parents that CPM is a known and manageable condition.
• Outline the diagnostic pathway. Describe the role of detailed ultrasound, CVS, and amniocentesis, including their timing, accuracy, and miscarriage risk (approximately 0.1–0.3% for CVS, 0.1–0.2% for amniocentesis). Be transparent about the risks and benefits of each
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