Vanishing Twin Syndrome: Causes, Signs and Effects
Vanishing twin syndrome was first recognized in 1945. Vanishing twin syndrome is when one of a set of twin/multiple fetuses disappears in the uterus during pregnancy. This is the result of a miscarriage of one twin/multiple. The fetal tissue is absorbed by the other twin/multiple, placenta or the mother. This gives the appearance of a “vanishing twin”.
How is Vanishing Twin Syndrome identified?
Before the use of ultrasound, the diagnosis of the death of a member of a multiple pregnancy was made through an examination of the placenta after delivery. Today, with the availability of early ultrasounds, the presence of twins or multiple fetuses can be detected during the first trimester. A follow-up ultrasound may reveal the “disappearance” of a twin.
For example, a woman may have an ultrasound at 6 or 7 weeks gestation. The doctor identifies two fetuses and the woman is told she is having twins. When the woman returns for her next visit, only one heartbeat can be heard with Doppler. A second ultrasound is conducted and only one fetus is observed.
Sometimes a woman may have symptoms that would indicate a miscarriage, yet, with an ultrasound, a single baby is found in her uterus. 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 21-30% of multifetal pregnancies.
What is the cause of Vanishing Twin Syndrome?
The cause of vanishing twin syndrome is frequently unknown. Abnormalities that result in the vanishing twin appear to be present from early in development rather than from a sudden occurrence. Analysis of the placenta and/or fetal tissue frequently reveals chromosomal abnormalities, while the surviving twin is usually normal. Improper cord implantation may also be a cause.
What are the effects of Vanishing Twin Syndrome on the mother and surviving twin?
If the loss occurs within the first trimester, neither the remaining fetus nor the mother has clinical signs or symptoms. The prognosis of the surviving twin is usually excellent, but it depends on the factors that contributed to the death of the other twin.
If the twin dies in the second or third trimester, there are increased risks to the surviving fetus. This could include a higher rate of cerebral palsy and a threat to the continuation of the pregnancy.
When a 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).
What are the signs of a possible Vanishing Twin Syndrome?
Research indicates more cases in women over the age of 30 years. Problems will usually begin early in the first trimester. The most common symptoms include bleeding, uterine cramps and pelvic pain.
What medical care is recommended 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 medical treatment. If the fetal death is in the second or third trimester, the pregnancy may be treated as high-risk. Cerebral palsy may result in the surviving twin.
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 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. 14
Emedicine from WebMD, http://www.emedicine.com
The Fetus Net, http://www.fetus.net
Williams Obstetrics Twenty-third Ed., Cunningham, F. Gary, et al, Ch 39