What is Vanishing Twin Syndrome?
Vanishing twin syndrome happens when one of two or more embryos in a pregnancy stops developing and eventually disappears. This can make it seem like the pregnancy has moved from having multiple babies to having just one, giving the impression of a ‘vanishing’ twin. In simple terms, this means that the number of babies originally seen in early pregnancy ultrasound scans is different from the number of babies born. This typically happens in pregnancies with more than one baby, often during the first three months (or first trimester).
A twin can be lost through a miscarriage, something the mother would be aware of, or through bleeding or light bleeding (spotting) early in the pregnancy, which would often go unnoticed because it’s a common occurrence during this period. The extent of this phenomenon may vary from the disappearance of an early gestational sac (the structure that holds the embryo) when it is still empty, to a sac that had begun to develop into a fetal pole (the beginning stage of the fetus), or even to a fetus with a documented heartbeat.
What Causes Vanishing Twin Syndrome?
In most cases, the reasons as to why a twin disappears, a condition known as vanishing twin, remain unclear. However, there are certain factors that are thought to be associated with the loss of the embryo. These factors include:
* The mother being over the age of 30
* Possible chromosome issues in the twin that passed away
* The application of methods to help reproduction such as in vitro fertilization (a process where an egg is combined with sperm outside the body)
* The likelihood of having more than one baby at a time
* A smaller than average placenta or other physical abnormalities of the placenta which may be linked to the loss of a twin in early stages
* Genetics and factors that can cause malformation of a developing fetus
Risk Factors and Frequency for Vanishing Twin Syndrome
The “vanishing twin syndrome” (VTS) is a phenomenon that wasn’t fully understood until ultrasound became common in medicine. VTS first came to light in 1945 when Stoeckel noticed that the number of multiple pregnancies (twins, triplets, etc.) was more than the actual birth rates of such pregnancies. This implied that a woman carrying multiple fetuses might lose one or more of them during pregnancy, sometimes before she even knows she is carrying more than one fetus.
With the use of ultrasound scans and transvaginal sonography early in pregnancy, detection of VTS has become more common. It’s estimated that VTS occurs in 36% of twin pregnancies and in 50% of pregnancies that start with three or more sacs.
In connection to assisted reproductive techniques (ART), which often lead to multiple pregnancies because they transfer more than one embryo to the uterus, the occurrence of VTS is estimated at 20-30%. As a consequence of VTS, babies that are born might have a very low birth weight and low APGAR scores, which are measures of a newborn’s health.
Signs and Symptoms of Vanishing Twin Syndrome
A “vanishing twin” pregnancy often shows symptoms such as vaginal bleeding or spotting, uterine cramps, or pelvic pain. These symptoms can indicate the loss of one of the babies during the first three months of pregnancy. This situation can potentially go unnoticed, and it’s usually referred to as a missed abortion or simply “vanishing”. It is commonly seen in women who are over 30 years old.
Women who conceive through assisted reproduction techniques (ART) are especially concerned about a vanishing twin pregnancy’s effects on the remaining baby. Due to these techniques, multiple embryos are often transferred into the uterus, which increases the chances of a twin pregnancy and, therefore, the possibility of a vanishing twin. Usually, there is a recorded history of fetal heart activity or more than one gestational sac reducing into a single pregnancy based on ultrasound findings during later pregnancy stages or at the point of delivery.
Testing for Vanishing Twin Syndrome
When a woman is pregnant with twins, certain examinations and tests can help detect if the ‘vanishing twin’ phenomenon is occurring. This phenomenon occurs when one twin disappears from the uterus during pregnancy. Ultrasonography, a type of imaging test, can be used during pregnancy to detect this. After the baby is born, examining the placenta can also provide details about the vanished twin.
One particular study looked at the levels of human chorionic gonadotropin (hCG), a hormone produced during pregnancy, in normal twin pregnancies and pregnancies experiencing the vanishing twin phenomenon. The results showed that hCG levels increase more slowly in vanishing twin pregnancies. This could be due to problems with the activity of cells that help with pregnancy (known as trophoblastic activity) that come from the embryo itself. The research suggested that any abnormality with hCG levels in vanishing twin syndrome happens early on, just after the embryos have implanted in the womb, and is not due to a sudden issue.
Another recent study involving a large number of pregnancies with vanishing twins looked at levels of two substances in the mother’s blood: pregnancy-associated plasma protein-A (PAPP-A) and B-human chorionic gonadotropin (B-HCG). The study aimed to determine if these could be used in first-trimester screening for chromosome disorders depending on the timing of the twin’s death and blood sampling. The results indicated that B-HCG levels didn’t change, but PAPP-A levels did increase in pregnancies where there was either an empty pregnancy sac or a deceased embryo.
If a pregnancy is due to assisted reproductive techniques, or the mother is older, there’s a higher chance of the vanishing twin phenomenon occurring. This is most likely due to the increased risk of abnormalities in the fetus’s chromosomes associated with the mother’s advanced age. Therefore, regular prenatal examinations, including ultrasonographic examinations and checks on maternal serum markers during the first and second trimesters, are strongly recommended.
Treatment Options for Vanishing Twin Syndrome
If one of the twins is lost during the first three months of pregnancy in what’s called a “vanishing twin” pregnancy, there are typically no special medical treatments necessary. However, the mom may experience symptoms like spotting or light bleeding and pelvic discomfort, which will need normal medical attention. The surviving twin often continues to grow normally and can usually be delivered without any problems.
However, if a twin is lost later in the pregnancy, during the second or third trimester, this could make the pregnancy high-risk. This is because losing a twin at this stage could potentially have negative effects on the surviving twin. In these cases, it’s important for the mom to have regular prenatal check-ups. These visits help the doctor track any signs of complications, and ensure the well-being of both the mom and the remaining baby. This can help mitigate any harmful effects on the mom’s health and the health of her baby.
What else can Vanishing Twin Syndrome be?
Using an ultrasound scan, doctors need to be very careful in diagnosing a ‘vanishing twin’ during early pregnancy. This is because there can be mistakes or artifacts that confuse the picture and might mistakenly suggest there is an extra pregnancy sac, or problems with the placenta. For example, cysts on the placenta can make it look like there are multiple pregnancies when there aren’t.
When such issues arise, it’s important to have professionals perform a microscopic examination of the placenta after the baby’s delivery to get accurate information.
What to expect with Vanishing Twin Syndrome
If one of the twins dies during the first three months of pregnancy, the survival chances of the other twin are usually very high. Actually, the health of the mother is not negatively impacted, apart from some light bleeding that she might experience. This bleeding could indicate the loss of the embryo early in pregnancy. In simpler words, if the loss of the fetus happens early, the mother might not even realize one of the twins is no longer there, because it doesn’t generally affect the health of the remaining fetus or the health of the mother.
Possible Complications When Diagnosed with Vanishing Twin Syndrome
If a baby is lost during the first three months of pregnancy, the period known as the embryonic stage, the mother may have complications associated with a phenomenon called the vanishing twin. These complications can take the form of vaginal bleeding, pelvic cramps, or back pain. The surviving baby, or co-twin, usually has good chances of survival in these instances.
However, if a twin is lost later during the pregnancy, the chances of complications for the remaining twin increase. These complications can include cerebral palsy, restricted growth within the womb, premature birth, and other birth defects often associated with a condition known as fetus papyraceous.
Recent research studied outcomes among pregnancies with a single baby, twins, and vanishing twins. This study found more negative outcomes in pregnancies with a vanishing twin compared to single baby and twin pregnancies. Moms with a vanishing twin had a higher likelihood of gestational diabetes, premature water-breaking, less amniotic fluid, weak cervix, induced labor, and early labor.
For the newborn baby, more birth abnormalities were found in cases of vanishing twin pregnancies compared to pregnancies with a single baby or twins. While cerebral palsy has no specific cause, it’s generally understood that a twin’s death late in a pregnancy increases the chances that the surviving twin will have cerebral palsy. Pregnancies involving in-vitro fertilization that experience vanishing twin syndrome demonstrate higher rates of early births and lower birth weights compared to those pregnancies that were only single babies from the start.
It is recommended that regular prenatal check-ups be conducted, and ultrasound screenings be used to identify potential abnormalities in pregnancies where a twin has been lost. Despite this, many pregnancies involving a vanishing twin proceed without complications throughout gestation and birth. However, research has shown that the surviving twin typically has a slightly lower birth weight compared to twins where both survive the pregnancy.
Preventing Vanishing Twin Syndrome
When a twin disappears during pregnancy, an event often referred to as a “vanishing twin,” most remaining pregnancies go smoothly. Nevertheless, it’s essential to address any parental anxieties about the health and prognosis of the surviving twin. Regular doctor visits during pregnancy are recommended in order to monitor the well-being of the leftover twin.
If the lost twin happened during the first three months of pregnancy, there’s typically no need for any special medical attention. The likelihood of the surviving twin being healthy is high, and the mother’s health should not be adversely affected. But if the twin is lost later on—in the second or third trimester (three to nine months)—the survival chances of the remaining twin can be threatened, and there may be a higher risk of birth defects, like cerebral palsy, which is a condition that affects muscle tone, movement, and motor skills.
It’s important that all relevant information about the factors that can contribute to a vanishing twin incident and the potential results are shared with the patient. This is to ensure that they are fully informed throughout the pregnancy.
