Knowledge | Vanishing Twin: An Often-Undetected Early Pregnancy Loss
Since 1945, doctors have increasingly recognized that some apparent singleton births began as twin pregnancies. During pregnancy, one fetus is lost through miscarriage, sometimes without the mother or doctor knowing. This is called a "vanishing twin" or "vanishing twin syndrome (VTS)."
In VTS, the lost fetal tissue is usually absorbed by the mother's body and the surviving fetus. Sometimes it can be identified by examining the surviving fetus's placenta. Ultrasound now allows earlier and more accurate diagnosis, revealing cases that previously went undetected.
1. How Common Is Vanishing Twin Syndrome?
One study found that about 36% of twin pregnancies experience VTS, rising to nearly half of higher-order multiple pregnancies. It may be becoming more common as assisted reproductive technologies such as in vitro fertilization (IVF) expand, because multiple fertilized eggs may be transferred and one or more may not survive to birth.
Another review of nine VTS studies found wide variation in reported rates. Limitations in ultrasound equipment or incomplete scans may leave some cases undetected. Timing is also important: without an early ultrasound, doctors may not know that a pregnancy began with twins.
2. Causes
VTS is usually caused by a chromosomal abnormality present at conception. Advanced maternal age (over 30), assisted reproduction such as IVF, placental abnormalities, and other fetal factors such as rubella infection may increase risk.
3. Risks
Risks to the Mother
Most mothers have no clear symptoms. A few experience spotting and cramping, which are common in early pregnancy. VTS in the first trimester generally requires no special measures. If it occurs in the second or third trimester, the pregnancy is usually classified as high risk and the mother and surviving fetus are monitored closely.
Risks to the Surviving Twin
Twin pregnancies generally carry more risk than singleton pregnancies, especially when the twins share a placenta. If the lost and surviving twins share a placenta, loss of one may affect the other's blood supply, so doctors use frequent ultrasounds to monitor the survivor.
Some studies suggest a higher risk of cerebral palsy among infants affected by VTS, but evidence is inconsistent. Overall, when each twin has a separate placenta—especially early in pregnancy—VTS usually has no adverse effect on the survivor.
4. Psychological Effects
Losing one twin is a distinct form of miscarriage and may cause profound grief. The surviving twin may sometimes experience guilt, and the family may benefit from counseling and other mental health resources.
Knowledge | Vanishing Twin: An Often-Undetected Early Pregnancy Loss
Knowledge | Vanishing Twin: An Often-Undetected Early Pregnancy Loss
Since 1945, doctors have increasingly recognized that some apparent singleton births began as twin pregnancies. During pregnancy, one fetus is lost through miscarriage, sometimes without the mother or doctor knowing. This is called a "vanishing twin" or "vanishing twin syndrome (VTS)."
In VTS, the lost fetal tissue is usually absorbed by the mother's body and the surviving fetus. Sometimes it can be identified by examining the surviving fetus's placenta. Ultrasound now allows earlier and more accurate diagnosis, revealing cases that previously went undetected.
1. How Common Is Vanishing Twin Syndrome?
One study found that about 36% of twin pregnancies experience VTS, rising to nearly half of higher-order multiple pregnancies. It may be becoming more common as assisted reproductive technologies such as in vitro fertilization (IVF) expand, because multiple fertilized eggs may be transferred and one or more may not survive to birth.
Another review of nine VTS studies found wide variation in reported rates. Limitations in ultrasound equipment or incomplete scans may leave some cases undetected. Timing is also important: without an early ultrasound, doctors may not know that a pregnancy began with twins.
2. Causes
VTS is usually caused by a chromosomal abnormality present at conception. Advanced maternal age (over 30), assisted reproduction such as IVF, placental abnormalities, and other fetal factors such as rubella infection may increase risk.
3. Risks
Risks to the Mother
Most mothers have no clear symptoms. A few experience spotting and cramping, which are common in early pregnancy. VTS in the first trimester generally requires no special measures. If it occurs in the second or third trimester, the pregnancy is usually classified as high risk and the mother and surviving fetus are monitored closely.
Risks to the Surviving Twin
Twin pregnancies generally carry more risk than singleton pregnancies, especially when the twins share a placenta. If the lost and surviving twins share a placenta, loss of one may affect the other's blood supply, so doctors use frequent ultrasounds to monitor the survivor.
Some studies suggest a higher risk of cerebral palsy among infants affected by VTS, but evidence is inconsistent. Overall, when each twin has a separate placenta—especially early in pregnancy—VTS usually has no adverse effect on the survivor.
4. Psychological Effects
Losing one twin is a distinct form of miscarriage and may cause profound grief. The surviving twin may sometimes experience guilt, and the family may benefit from counseling and other mental health resources.
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