How Vanishing Twin Affects Prenatal DNA Testing

Rewritten on: June 25, 2025

Vanishing twin is a phenomenon in which one of a multiple pregnancy spontaneously disappears in early pregnancy, and it can affect the results of prenatal DNA testing (NIPPT) and non-invasive prenatal testing (NIPT). This article explains the causes, effects on testing, and precautions for continuing the pregnancy in detail.

What Is Vanishing Twin

Vanishing twin is a phenomenon in which one fetus of a multiple pregnancy spontaneously disappears in early pregnancy. It is typically discovered when an initial ultrasound confirms twins (or triplets or more), but a subsequent scan shows that one of the fetuses is no longer present. In most cases, the tissue of the vanished fetus is absorbed by the mother's body or incorporated into the placental tissue of the remaining fetus (1).

Vanishing twin tends to occur between roughly weeks 6 and 8 of early pregnancy, and the remaining fetus is usually not significantly affected. Research indicates that vanishing twin occurs in about 21–30% of naturally conceived multiple pregnancies, and this phenomenon has come to be observed more frequently as ultrasound scans have become more common due to the spread of in vitro fertilization (IVF) (2). That said, when vanishing twin is suspected, further detailed examination may be recommended to accurately confirm the progress of the pregnancy and the health of the fetus.

When vanishing twin occurs, the mother may experience mild bleeding or abdominal pain, but these symptoms usually resolve on their own. On the other hand, if one fetus disappears after the second trimester, the effect on the remaining fetus can be greater, so more careful monitoring is required (3).

Causes of Vanishing Twin

The main causes of vanishing twin are believed to be genetic abnormalities and developmental failure in the fetus. Specifically, numerical chromosomal abnormalities (such as trisomy or monosomy) are frequently observed in the fetus that vanishes, and it has been reported that this prevents normal cell division and organ formation, leading to natural disappearance (1).

In addition, as in vitro fertilization (IVF) technology has advanced, multiple pregnancies have increased, and along with this, cases of vanishing twin are also said to be increasing. In IVF, multiple fertilized eggs have historically been transferred, which raises the rate of multiple pregnancy compared with natural conception. In recent years, single embryo transfer (SET) has increasingly been recommended, but the risk of identical twins arising from splitting still remains (4).

The main causes of vanishing twin can be summarized as follows.

• Chromosomal abnormalities in the vanishing fetus (trisomy, monosomy, etc.)
• Poor implantation position of the embryo or abnormal placenta formation
• Increase in multiple pregnancies due to IVF
• Uterine environment or immunological factors on the mother's side
• Developmental failure during the division process of the fertilized egg

These factors may act alone or in combination. In any case, it is important to understand that vanishing twin is not the result of any fault on the mother's part, but rather a phenomenon that occurs as part of the natural reproductive process.

Prenatal DNA Testing and Non-Invasive Prenatal Testing

DNA testing during pregnancy is broadly divided into two categories depending on its purpose.

The first is "Prenatal DNA Testing (NIPPT)," which identifies the father of the fetus by analyzing fetal DNA present in the mother's blood (cell-free fetal DNA, or cffDNA). NIPPT analyzes fetal-derived DNA fragments contained in blood drawn from the mother using a next-generation sequencer (NGS) and compares them with the DNA of the candidate father to determine the parent-child relationship (5).

The second is "Non-Invasive Prenatal Testing (NIPT)," which reveals the risk of chromosomal abnormalities such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). NIPT analyzes the fetal-derived components within the mother's cell-free DNA to screen for whether a particular chromosome is present in greater number than normal (trisomy) (6).

Unlike invasive procedures such as amniocentesis or chorionic villus sampling, neither test carries a risk of miscarriage, which is why the number of these DNA tests performed has surged in recent years, particularly in Europe and the United States. NIPT in particular has demonstrated high accuracy, with a sensitivity (detection rate) of over 99% for trisomy 21 screening, and is increasingly recognized worldwide as a standard screening method (6).

Find out who the father is while the baby is still in the womb

Check the risk of genetic disorders in your unborn baby

Learn more about non-invasive prenatal testing here

How Vanishing Twin Affects DNA Testing

When vanishing twin occurs, it can affect the results of NIPPT or NIPT. Because DNA from the vanished fetus can remain in the mother's blood, it can cause confusion in the test results. It has been pointed out that the cell-free DNA of the vanished fetus may continue to remain in the mother's blood for several weeks after the disappearance (3).

For example, if the fetal DNA detected during a paternity test (NIPPT) turns out to be that of the vanished fetus, it can be difficult to demonstrate the correct parent-child relationship. In unusual cases where the remaining fetus and the vanished fetus are twins with different fathers, the detected DNA profile becomes more complex, and additional verification may be needed for the determination.

Also, with non-invasive prenatal testing (NIPT), if the vanished fetus had a chromosomal abnormality, its DNA may be detected, potentially leading to an incorrect assessment of genetic disease risk even though the surviving fetus is actually healthy. This is known as one of the causes of "false positives," and it is recommended that the presence of vanishing twin be confirmed during counseling prior to NIPT (7).

In such situations, it is important to consult with a physician. In some cases, additional definitive testing (such as amniocentesis or chorionic villus sampling) may be necessary.

The main effects of vanishing twin on DNA testing can be summarized as follows.

Continuing Pregnancy After Vanishing Twin

When vanishing twin is confirmed, care is needed from a medical, psychological, and lifestyle standpoint. Losing one fetus in early pregnancy can place a significant emotional burden on the mother, even if the remaining fetus is healthy.

Here is a step-by-step guide to the recommended approach for continuing pregnancy after vanishing twin.

1. Regular ultrasound examinations: Continuously monitor the growth and development of the remaining fetus to enable early detection of any abnormalities.
2. Checking the mother's health: Thoroughly manage the mother's condition by checking nutrient intake and hormone balance as needed.
3. Securing psychological support: Share feelings with family and friends, and receive support from a professional counselor when needed to help reduce stress.
4. Consulting a specialist institution before DNA testing: If undergoing prenatal DNA testing or NIPT, informing the testing institution about the vanishing twin situation in advance makes it easier to obtain accurate results.
5. Close communication with your physician: Maintain close communication with your obstetrician-gynecologist and establish a system so you can consult immediately if you experience abnormal symptoms such as bleeding or abdominal pain.

By taking various measures to maintain the health of both the mother and the remaining fetus, you can continue the pregnancy with peace of mind.

Prenatal parentage DNA testing is a useful method for identifying the father during pregnancy in a way that is safe for both the fetus and the mother, but if testing is performed without disclosing a special circumstance such as vanishing twin, it can cause confusion in the testing process and delay delivery of the correct result. We ask for your cooperation in contacting us before testing begins, as this allows us to report accurate results more quickly.

In February 2025, seeDNA plans to launch a specialized DNA test for detecting vanishing twin in babies after birth. This test uses advanced analytical technology to detect traces of the vanished fetus's DNA in the tissue or blood of the surviving fetus, offering a new service for those who wish to confirm vanishing twin after birth.

Frequently Asked Questions

Q1. How likely is vanishing twin to occur?

A. Vanishing twin is said to occur in about 21–30% of multiple pregnancies. In recent years, it has been detected more frequently due to improvements in ultrasound technology and the spread of in vitro fertilization [ref:2]. It can also occur in natural pregnancies and is not the result of any fault on the mother's part.

Q2. Does vanishing twin affect the surviving fetus?

A. When vanishing twin occurs in early pregnancy (around weeks 6–8), there is usually almost no effect on the surviving fetus. However, if it occurs after the second trimester, the effect on the surviving fetus may be somewhat greater, so it is important to monitor progress with regular ultrasound examinations [ref:3].

Q3. If vanishing twin has occurred, can I still have NIPT (non-invasive prenatal testing)?

A. Even if vanishing twin has been confirmed, it is still possible to undergo NIPT, but DNA from the vanished fetus may remain in the mother's blood and cause a false positive. For this reason, it is recommended that you always inform your physician or the testing institution of the vanishing twin history before testing and receive a thorough explanation of how the results should be interpreted [ref:7].

Q4. Are there any precautions when undergoing prenatal DNA testing (NIPPT) after vanishing twin?

A. Prenatal DNA testing (NIPPT) analyzes fetal-derived DNA in the mother's blood, but in some cases the mixture of DNA from a vanished fetus can complicate the test results. By sharing information about the vanishing twin situation with seeDNA before testing begins, we can select the appropriate analysis method and deliver accurate results more quickly.

Q5. How should I handle the emotional side of things if vanishing twin occurs?

A. Because vanishing twin often occurs in early pregnancy, the physical effect on the mother is usually limited, but many people experience significant emotional distress. In addition to talking with family and friends, it is recommended to seek psychological support from an obstetrician-gynecologist or counselor as needed. Please don't try to bear it alone — make active use of the support available around you.

Q6. Does seeDNA offer any specialized testing related to vanishing twin?

A. Starting in February 2025, seeDNA plans to launch a specialized DNA test for detecting vanishing twin in babies after birth. This is an advanced test that uses high-precision next-generation sequencer (NGS) technology to detect traces of the vanished fetus's DNA. Please feel free to contact seeDNA for more details.

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