What causes vanishing twin syndrome?

It can occur due to genetic abnormalities, issues with the placenta, or other early pregnancy complications.

How do you know if you had a vanishing twin?

Many pregnant individuals may not notice any symptoms. It is usually confirmed when early ultrasounds show two embryos, but later scans reveal only one.

Vanishing Twin Syndrome: What Happens When One Twin Stops Developing

In the early weeks of your pregnancy, your doctor might have informed you that you were expecting twins. Your happiness must have doubled at the thought of two little ones on the way. But during a follow-up visit or ultrasound, your doctor may have shared something unexpected: a diagnosis called vanishing twin syndrome (VTS).

Hearing this can feel confusing and heartbreaking. You may wonder why it happened, worry about your surviving baby, or feel a sense of loss for a life you had just begun to imagine. It’s important to know that these feelings are completely natural. Learning about this syndrome can give you clarity and help you understand what to expect during your pregnancy.

What is Vanishing Twin Syndrome (VTS)?

Vanishing twin syndrome happens when one twin is lost early on during the pregnancy, and the other twin continues to develop. The lost twin’s tissue is often reabsorbed by your body, the surviving twin, or the placenta. This makes it seem like the twin has “vanished.”

VTS was first noticed around 1945, but doctors can now spot it more easily with modern ultrasounds. An early ultrasound might show two embryos, but a later one shows only one, confirming VTS. It affects about 36 per cent of twin pregnancies and up to 50 per cent of pregnancies with three or more babies.

Why Does Vanishing Twin Syndrome Happen?

The exact reasons for VTS aren’t fully clear, but there are some known causes:

Chromosomal issues: One twin may have abnormal chromosomes from conception.
Improper cord implantation: The twin may not get enough nutrients to develop if the umbilical cord doesn’t attach properly.
Maternal factors: Infections like rubella or autoimmune conditions can increase the risk.
Environmental factors: Exposure to toxins or radiation might play a role, though this is less common.

Who Is More Likely to Experience Vanishing Twin Syndrome?

Certain factors make VTS more likely:

Older age: If you’re over 30, your chances of having twins and VTS are higher.
Fertility treatments: Procedures like in vitro fertilisation (IVF) often involve transferring multiple embryos, which increases the risk of VTS.
Placental abnormalities: Problems with the placenta can affect one twin’s development.
Health conditions: Issues like diabetes or obesity can raise the risk of complications in multiple pregnancies.

Signs and Symptoms of Vanishing Twin Syndrome

Vanishing twin syndrome happens without any obvious signs, especially in the first trimester. You might still feel pregnant because your body continues producing pregnancy hormones for the surviving twin. But the following symptoms may suggest VTS:

Light bleeding or spotting: This can happen, but is often mistaken for normal early pregnancy changes.
Mild cramping: You might feel some cramps as your body adjusts to the loss.
Sudden drop in pregnancy symptoms: Though rare, if nausea or breast tenderness suddenly decreases, it could be a clue.

How Vanishing Twin Syndrome Is Diagnosed

VTS is usually found through routine ultrasounds. This is how doctors confirm it:

Ultrasound scans: An early scan might show two embryos or sacs, but a later one shows only one. This is the main way VTS is diagnosed.
Blood tests: Checking levels of the pregnancy hormone hCG can sometimes hint at a loss, but it’s not precise enough on its own.
Genetic testing: In some cases, doctors may test for chromosomal issues in the surviving twin if complications are suspected.

Poor ultrasound equipment or incomplete scans can sometimes miss VTS, so it’s important to have regular check-ups with a skilled healthcare professional. You might not even know you were carrying twins without an early ultrasound.

How Does Vanishing Twin Syndrome Affect Your Pregnancy?

Most pregnancies with VTS continue without any major issues, and the vanishing twin effect on the surviving twin is usually minimal. However, there are some things to keep in mind:

First trimester loss: If VTS occurs early, the surviving twin usually develops normally, and no special treatment is needed.
Later loss: If the loss happens in the second or third trimester, your pregnancy might be considered high-risk.
Shared placenta risks: If the twins shared a placenta, the surviving twin might face issues like uneven blood flow.
Increased risks: You might have a higher chance of gestational diabetes, early labour, or low amniotic fluid. The surviving twin could also have a lower birth weight or lower Apgar scores (a test of a baby’s condition at birth).

Emotional Impact of Vanishing Twin Syndrome and How to Cope

Losing a twin can be heartbreaking, even if it happens early. It’s normal to feel sadness, guilt, or confusion. This is what you should know:

No matter how early the loss happens, it’s okay to feel upset. Every parent processes this differently.
Talking to a counsellor or joining a support group can help you work through your feelings. Your doctor can suggest resources.
Later in life, the surviving twin might feel guilt or wonder about their lost sibling. Counselling can help them too.

Don’t feel pressured to “move on” quickly. Give yourself time and seek support from loved ones or professionals if needed.

Can You Prevent Vanishing Twin Syndrome?

Unfortunately, there’s no way to prevent VTS as it’s often due to factors beyond your control. Even with a healthy lifestyle, it can still happen. However, you can reduce overall pregnancy risks by:

Staying healthy and eating a balanced diet.
Avoiding harmful substances like alcohol, tobacco, and toxins.
Attending regular check-ups to catch any issues early.
Keeping conditions like diabetes or obesity under control with your doctor’s help.

Experiencing vanishing twin syndrome can be an emotional and difficult part of a twin pregnancy. While it is often beyond your control, most pregnancies continue without complications, and the surviving twin generally grows into a healthy baby.

Whether you’re pregnant, a new mom, or navigating postpartum, you don’t have to do it alone. Join our support group to connect, share, and support one another.

FAQs on What Happens When One Twin Stops Developing During Pregnancy?

What causes vanishing twin syndrome?
It can occur due to genetic abnormalities, issues with the placenta, or other early pregnancy complications.
How do you know if you had a vanishing twin?
Many pregnant individuals may not notice any symptoms. It is usually confirmed when early ultrasounds show two embryos, but later scans reveal only one.