Your pregnancy and baby guideAntenatal care with twins

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Because there are increased risks with a twins or triplet pregnancy, especially if your babies share a single placenta, good antenatal care is essential.

Check-ups and scans in a twin pregnancy

The number of tests and scans you’ll be offered will depend on the type of twins or triplets you're having. Women with multiple pregnancies should be offered an ultrasound scan from 11 weeks 0 days to 13 weeks 6 days, and it's important to attend this appointment.

This is the best time to find out what type of placenta and membranes your twins have (chorionicity) and check your dates. You can also have a nuchal translucency test for Down's syndrome done at the same time if you wish.

Read more about screening for Down's syndrome.

If you have an early scan, it's possible you'll see two foetal heartbeats and two foetal sacs, but one will have disappeared by the 12-week scan.

This is because one of the embryos failed to thrive and it’s been reabsorbed into the womb. This is referred to as vanishing twin syndrome and has no physical effect on the surviving baby.

You’ll also be offered a scan around 18 to 21 weeks to check that your babies are developing normally.

Different types of twins

For medical purposes, there are three types of twins. These apply to triplets too, although a triplet pregnancy will be more complex than a twin one. The three types are:

  • dichorionic diamniotic (DCDA) twins – each has their own separate placenta with its own separate inner membrane (amnion) and outer membrane (chorion) 

  • monochorionic diamniotic (MCDA) twins – share a single placenta with a single outer membrane and two inner membranes

  • monochorionic monoamniotic (MCMA) twins – share both the inner and outer membranes

All non-identical twins are DCDA, and a third of identical twins are DCDA. The other two thirds of identical twins are MCDA, and just 1% of identical twins are MCMA.

The percentages of identical and non-identical twins born in the UK aren't routinely recorded, but according to the Multiple Births Foundation about one third of twins are identical.

What extra care may I need?

If your babies are MCDA, you can expect more scans and monitoring, as this type of twins has the highest risk of twin-twin transfusion syndrome (TTTS), which is an abnormality of the placenta.

You may be referred to a regional centre for foetal medicine to be seen by a specialist doctor.

If your babies are MCMA, you’ll also have frequent scans. With this type of twins there’s often some cord entanglement, which can cause complications.

These types of twins are rare and you can expect to receive specialist care and close monitoring. You should be seen by a foetal medicine specialist who has cared for MCMA twins before. This type of twins are usually delivered at 32 to 33 weeks pregnant.

If your babies are DCDA, the risks to their health in the womb are much lower. You'll usually be scanned every four weeks.

It's important to attend all your appointments, so any problems can be picked up early and treated if necessary.

Find out more about antenatal checks and tests.

Risks in twin pregnancies

While most multiple pregnancies are healthy and result in healthy babies, there are more risks to be aware of when you are pregnant with two or more babies. If you're pregnant with more than one baby, you're at higher risk from pregnancy complications, such as anaemiapre-eclampsia and gestational diabetes.

Make sure you go to all your antenatal appointments, so any problems can be picked up early and treated if necessary. Twins and triplets have a higher risk of being born prematurely (before 37 weeks) and having a low birth weight of under 2.5kg (5.5lb). Triplets have a 94% chance of being born prematurely and of having a low birth weight.

Being premature increases the risk of problems after birth, such as breathing difficulties. Your obstetric team will work closely with you throughout your pregnancy and after your babies are born to help make sure you and your babies are safe and healthy.

Twin-twin transfusion syndrome

TTTS affects identical twins who share a placenta (monochorionic). The risk is higher for MCDA twins, but it can occur in MCMA twins too.

It’s caused by abnormal connecting blood vessels in the twins' placenta. This results in an imbalanced blood flow from one twin (known as the donor) to the other (recipient), leaving one baby with a greater blood volume than the other.

TTTS affects 10-15% of monochorionic twins and can have serious consequences. You'll need to discuss your individual case with your doctor, as what works in one TTTS pregnancy may not be appropriate in another.

Go to the Tamba website for more information on TTTS.

Page last reviewed: 19/04/2016
Next review due: 19/04/2019