Until around 1945, we did not know about Vanishing Twin Syndrome. Twin pregnancy losses went undetected before the days of early ultrasounds. But even though it was formally recognised and named in the mid forties, many women over the preceding generations must have been aware they were pregnant with twins but had miscarried one of them early in the pregnancy. Sometimes this became obvious when the placenta was examined after birth and the midwife or obstetrician told the mother about the other baby which did not develop.
When Vanishing Twin Syndrome occurs, the remains of the foetal tissue are absorbed by the remaining twin, the mother or even the placenta. Now, with the common use of ultrasounds during pregnancy, embryos can be seen at their earliest, cellular level. This has meant that from almost the moment of implantation women can potentially become aware they are pregnant with twins.
Early confirmation of multiple pregnancy is relatively easy when two or more embryonic sacs, rather than one, are seen on the ultrasound screen. The earliest stage when foetal heartbeats can be visualised is at around six weeks of gestation. But when subsequent ultrasounds after the initial one are carried out and only one viable sac can be seen, or only one heartbeat heard, then the diagnosis of Vanishing Twin Syndrome is given.
Diagnosing a twin pregnancy is more common since the widespread use of fertility assistance and closer pregnancy monitoring. When checking and counting is done on the numbers of fertilised eggs implanted and, their subsequent growth so carefully monitored, it is easier to see when something has gone wrong.
The word “vanishing” is rather a magical term for what is essentially, a rather sad occurrence. Because the twin and pregnancy sac is reabsorbed by the mother, the word “vanishing” is used to describe this. If the miscarriage happens very early on in the pregnancy, there are no outward signs.
The truth is that we are not 100% sure why it happens but many explanations have been put forward.
It is thought that conception with twins or multiples occurs much more often than we are aware of. Women over the age of 30 are more likely to experience Vanishing Twin Syndrome. A conservative estimate is that it happens in around 21-30% of multiple pregnancies.
There is nothing which can be done to prevent this from occurring. The major cause is thought to be an interruption to the embryo’s developing genetic structure. This is completely out of the control of the mother or her partner.
In cases of repeated miscarriage, for no obvious reason, genetic counselling may become necessary. Speak with your health care practitioner if this is an option you wish to investigate.
If it occurs in the first trimester of pregnancy, there are often no symptoms at all. The mother continues to feel pregnant because she still has sufficiently high levels of hCG, the pregnancy hormone, to sustain the viable embryo.
However, if she has conceived through fertility assistance and is having regular blood tests, there is likely to be a reduction noted in her circulating pregnancy hormones. This may be the earliest indication that a mother was pregnant with twins or triplets, but one of them has miscarried.
Unlike a miscarriage though, the pregnant mother may not have any vaginal bleeding or uterine cramping, though some still may. This really depends on the stage of pregnancy when the miscarriage occurs.
It’s easy for mothers to interpret vaginal bleeding as a complete miscarriage and an indication that they are no longer pregnant. But if twins or triplets have been conceived and only one of them miscarried then the other twin/triplet is likely to mature in the usual way.
Unless a mother has been told she is pregnant with twins or multiples, she may not even be aware she has miscarried with one of them. If, however, one of the embryos dies in the second or third trimester there can be some increased risks with the remaining one. Premature birth can become a higher risk as can the risk of cerebral palsy.
If the miscarriage occurs before eight weeks of gestation, the water and fluids from the miscarried embryo are reabsorbed and there is nothing to be seen. But if the miscarriage happens after this time, the tiny, compressed foetus can sometimes be seen at the birth of the other twin as they are both expelled from the uterus. This may be the first indication that twins were initially conceived though only one matured to delivery.
Sometimes a second or third trimester miscarriage of one twin can cause significant obstetric problems. Premature labour, infection, bleeding and an increased risk of birth complications can all occur with a late stage miscarriage of one twin.
After the death of one twin the other, viable one is usually not impacted. Though this depends on the reason why the miscarriage occurred in the first place. If it was because of the individual embryo’s chromosomal or genetic makeup, then this will not necessarily impact on the other twin – particularly if they were dizygotic or fraternal twins.
In the majority of cases, the surviving twin is not affected by the miscarriage of the other. They continue to grow and mature to full gestation without any complications. However, recent studies have found that around 7% of women who have experienced Vanishing Twin Syndrome will deliver the other baby or babies prior to 28 weeks of gestation. There is also an increased risk of the surviving baby or babies having low birth weight and the health risks associated with this. There is also potentially a greater risk of the surviving twin/triplet having health issues later in life.
If your health care practitioner is aware of your Vanishing Twin Syndrome they will monitor your pregnancy extra carefully. If you are an Rh Negative blood group your blood will be tested for antibodies. You may need to have an injection of Anti D after your baby is born to protect any future babies you may carry.
There is no specific treatment. If the other twin continues to mature and develop towards maturity, there is no management for the twin which has died. If it becomes clear that both twins are no longer viable and no heartbeats can be seen, then a dilatation and curette of your uterus may become necessary.
Absolutely, no matter how early or late in gestation a miscarriage occurs, it is entirely appropriate for parents to feel sad. Allow yourself time, reflection and if necessary, counselling to work through your feelings. There is no one “right” way to feel about the loss of a baby or pregnancy and every mother’s experience is unique. Comparisons and feeling the pressure of “having” to put on a brave face can be exhausting.
Speak with your GP, midwife or obstetrician about counselling options, or check the Sands New Zealand website or ring them on 0800 726374 for specific guidance and support.