Vanishing Twin Syndrome is when there is a sudden, spontaneous loss of a baby in a multiple pregnancy, leading to a normal single pregnancy. Also called the Disappearing Twin Syndrome, this is a type of miscarriage. Diagnosis of this condition began after ultrasound technologies (the only way to know you are carrying twins early in your pregnancy) were developed and routinely underwent for mothers to see their babies. In some cases, doctors and parents noticed that two gestational sacs were detected at first, but later, only one foetus survives and can be detected, as the second disappears.
How often does this happen?
Vanishing twins is quite common especially in multiple pregnancies with two gestations which is 36% risk and more than 50% risk with three or more gestations. The risks could be higher as the condition could possibly occur undetected during the first trimester – before a doctor can hear the fetal’s heartbeat or the mother’s acknowledgement of having twins. In fact, the risks could be higher as the condition could possibly occur undetected.
When this happens, the vanishing embryo usually stops developing and the tissue is absorbed back into the uterus, seemingly having disappeared. Sometimes, the embryo can become ‘mummified’ and leave behind small cysts on the placenta. In rare cases, a teratoma tumour (where there is some remains of fetal tissue) may occur in the surviving twin, nevertheless this is harmless to the baby. The risk of vanishing twin decreases greatly when you reach the second trimester, down to only 3%.
What caused this syndrome?
A vanishing baby can cause much grief and confusion for parents who are told to be expecting twins or triplets. While the cause of this syndrome in most cases is still unknown, studies have shown that the surviving twin is usually healthy, while the vanishing one may have chromosomal abnormalities. Improper cord implantation has also been cited as one of the possible causes.
Australian researchers have also attributed this increased risk of birth defects in multiple pregnancies to infertility treatments, which are becoming increasingly common and able to increase the chance of twins or triplets. However, there is also a study that suggests that this condition happens more often in natural conception than in-vitro fertilisation, estimating an 18.2% risk of this condition in multiple pregnancies without fertility treatments.
What can you do about this?
If the condition occurs during the first trimester, the mother will usually go on to deliver the surviving baby without any complications, but if the twin vanishes in the second or third trimester, the mother may be at the risk of infection, hemorrhage or preterm labor, while the surviving baby may be at risk of cerebral palsy or intrauterine growth restriction – so your doctor will monitor you and your baby’s health even closer.
Often, there are not many symptoms of this condition, but if you have abnormal hCG levels, vaginal bleeding, cramping and pelvic pain, contact your doctor immediately.
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