After the developing twin disappears, its fetal tissue is absorbed by the surviving baby and its mother. With a parasitic twin, two embryos begin developing together. Then, one of the embryos stops developing, as with vanishing twin syndrome. Hard statistics about vanishing twin are limited in scope. Part of that is because ultrasound technology, which has given us insight into how common vanishing twin might be, is fairly new.
That means that in many cases of vanishing twin, parents and doctors never know. At least one study suggests that vanishing twin happens more after natural conception of twins than in cases of in vitro fertilization. That same study estimates that This kind of loss is instead considered a late-term miscarriage. Causes and statistics for late term miscarriages vary widely. There are some pregnancy symptoms that could indicate vanishing twin syndrome.
Light spotting called implantation bleeding occurs in many healthy pregnancies. An hCG level that starts out high and then plateaus could indicate that one fetus has stopped developing.
From what we know about this condition, vanishing twin happens for the same reason most early miscarriages occur — something called chromosomal abnormality. During this process, chromosomes can be switched or left out of cells completely. When this happens, a miscarriage occurs. This means that one fetus can keep growing after its twin stops developing. Vanishing twin syndrome is usually found during an ultrasound appointment. An ultrasound is typically first performed between 8 and 12 weeks of pregnancy, during which time you might see two or more heartbeats on the ultrasound screen.
However, some mothers experience symptoms similar to miscarriage , including:. The only sign of vanishing twin syndrome may be a later ultrasound that shows that there are no longer two fetuses in the womb. Even if you have symptoms that are similar to those of a miscarriage, none are a sure sign of a pregnancy loss.
Women who have in vitro fertilization — in which one or more fertilized eggs are placed in your uterus in the hopes that one of them will implant and become a pregnancy — may have a higher risk of vanishing twin syndrome than those who conceive naturally. Women over 30 may also be more likely to experience vanishing twin syndrome. However, that might be because older mothers, in general, have higher rates of multiple pregnancies.
In many cases, when vanishing twin syndrome occurs in the first trimester, the mother goes on to experience a normal pregnancy and delivers the single healthy baby without complication or intervention. If a twin dies in the second or third trimester, the remaining baby may be at an increased risk of intrauterine growth restriction IGR , and the mother may be at risk of preterm labor, infection or hemorrhaging. In this case, your practitioner will carefully monitor the health and growth of your remaining twin and watch you closely for signs of complications.
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The educational health content on What To Expect is reviewed by our medical review board and team of experts to be up-to-date and in line with the latest evidence-based medical information and accepted health guidelines, including the medically reviewed What to Expect books by Heidi Murkoff.
This educational content is not medical or diagnostic advice. Use of this site is subject to our terms of use and privacy policy. One baby does not develop at the same rate as the other, and the tissue of the less-developed baby reabsorbs into your womb, sometimes before you even realize you were pregnant with twins in the first place. The other fetus usually continues to grow and develop appropriately through the entire gestation period.
Women older than 30 years old have a higher risk of experiencing vanishing twin syndrome than younger mothers. Some women do not show any signs of trouble, while others experience cramping and bleeding consistent with miscarriage. Miscarriage of one baby in a multiple pregnancy is still possible after the first trimester. Losses later into the pregnancy may still be considered vanishing twin syndrome, but this is rare.
The more likely reason for you to miscarry one fetus while remaining pregnant with the other is an abnormality of the placenta or umbilical cord, or a disorder in the child that becomes fatal. The exact nature of the miscarriage will determine how the pregnancy proceeds; you may be put on bed rest to protect the remaining baby as much as possible until your due date. Reduction of a pregnancy is not a miscarriage in the strict sense of the word; miscarrying means that your baby has died spontaneously without action on your part.
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