Vanishing twin syndrome was first recognized in 1945. This occurs when one of a set of twin or multiple fetuses ‘disappears’ inside the uterus during pregnancy.
This is the result of a miscarriage of one twin/multiple. The fetal tissue is re-absorbed by the other twin/multiple, placenta or the mother. This gives the appearance of a “vanishing twin”.
How is Vanishing Twin Syndrome diagnosed?
Before the use of ultrasound, the diagnosis of the death one of babies in a multiple pregnancy was made through an examination of the placenta after delivery. Today, with the availability of early ultrasounds, the discovery of twins or multiple fetuses can be detected early during the first trimester. A later follow-up ultrasound may reveal the “disappearance” of a twin that had shown up earlier on the scan.
For example, a woman may have an early ultrasound at six or seven weeks of pregnancy. The doctor identifies two fetuses on the screen, and the woman is then told she is having twins. When the mother comes back for her next visit, only one heartbeat can be heard with Doppler. A second ultrasound is conducted and only one baby is seen this time. Emotionally this can be very hard on the mother, due to knowing previously that there was another baby. She may have just adjusted to planning for twins, and now must adjust to losing one.
Sometimes a woman may have symptoms that would indicate a miscarriage and loss of a baby and yet, with an ultrasound, a single baby is found with a strong heartbeat, indicating that initially there may have been more than one .
Vanishing twin syndrome has been diagnosed more frequently since the use of ultrasonography in early pregnancy. A conservative estimate of frequency is that vanishing twin syndrome occurs in about 21-30% of multi-fetal pregnancies.
The cause of vanishing twin syndrome is usually unknown. Abnormalities that result in the vanishing twin appear to be present from early in development rather than from a sudden occurrence, similar to miscarriage of a singleton baby. Analysis of the placenta and/or fetal tissue frequently reveals there were pre-existing chromosomal abnormalities, while the surviving twin is usually normal. Improper cord implantation may also be a possible cause.
How does vanishing twin syndrome affect the mother and remaining baby ?
If the loss occurs within the first trimester of the pregnancy, neither the remaining fetus nor the mother has clinical signs or symptoms. The prognosis of the surviving twin is usually excellent, but it does depend on the reasons that contributed to the death of the other twin. If the twin dies in the second or third trimester, there are some increased risks to the surviving fetus. This could include a higher rate of cerebral palsy and a threat to the continuation of the pregnancy. This can be extremely devastating to the expectant mother.
When one twin dies after the embryonic period of gestation (eight weeks), the water within the twin’s tissues, the amniotic fluid, and the placental tissue may be reabsorbed. This results in the flattening of the deceased twin from the pressure of the surviving twin. At delivery, the deceased fetus may be identified as fetus compressus (compressed enough to be noticed) or as fetus papyraceous (flattened remarkably through loss of fluid and most of the soft tissue).
Are there any risks for possible Vanishing Twin Syndrome?
Research indicates more cases occur in women over the age of 30 years, as do more twin pregnancies in general.
Problems will usually begin early in the first trimester. The most common symptoms include bleeding, uterine cramps and pelvic pain.
Is there specific medical care needed for Vanishing Twin Syndrome?
No special medical care is necessary with an uncomplicated vanishing twin in the first trimester. Neither the surviving twin nor the mother would require any specialized medical treatment. If the fetal death is in the second or third trimester, the pregnancy may be treated as high-risk. Cerebral palsy is a possible result in the surviving twin.
All pregnant women should seek medical care if they are experiencing bleeding, cramping and pelvic pain. They should be evaluated at a place with ultrasound capabilities. The use of an ultrasound is very important to determine that no viable fetus remains before deciding if a D&C; might be indicated. The woman can choose to wait for a natural miscarriage in many cases.
Compiled using information from the following sources:
Danforth’s Obstetrics and Gynecology Ninth Ed., Scott, James R., et al, Ch. 14Emedicine from WebMD, http://www.emedicine.com MedicineNet, http://www.medterms.comThe Fetus Net, http://www.fetus.net Williams Obstetrics Twenty-third Ed., Cunningham, F. Gary, et al, Ch 39