Pregnancy Guide

Antenatal care with twins

Because there are increased risks with a twin 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 will be offered will depend on the type of twins or triplets you're having. Women with multiple pregnancies should be offered an early pregnancy dating scan scan from 11 weeks 2 days to 14 weeks 1 day, 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 screening test for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome done at the same time if you wish. This is done by measuring the small space at the back of the babies’ necks, called a nuchal translucency (NT), and a blood test taken around the same time. Screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome is more complicated in twin pregnancies so ensure that you discuss your options before having the blood test with your obstetrician (hospital doctor), or midwife specialising in screening in twin pregnancies in the hospital where you are having your care.

Read more about screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome here and there is a film clip available here to give you more information. Please view the film clip before attending your booking appointment with your midwife, you will be more prepared for the discussions you will have on screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome.

You will also be offered an anomaly scan around 18 to 21 weeks to check that your babies are developing normally.

Occasionally early in a multiple pregnancy only one fetus thrives.  If you have an early scan, it's possible you'll see two fetal heartbeats and two fetal sacs, but one will have disappeared by the early pregnancy dating scan.  This is because one of the embryos failed to thrive and it has been reabsorbed into the womb. This is referred to as vanishing twin syndrome and has no physical effect on the surviving baby.

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

The percentage 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 monochorionic diamniotic (MCDA), you can expect more scans and monitoring as this type of twins has the highest risk of twin-twin transfusion syndrome (TTTS), an abnormality of the placenta.

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

If your babies are MCMA, you will also have frequent scans. With this type of twins there is 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 will 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 anaemia, pre-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 90% 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 and cerebral palsy. 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)

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 is 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 to 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.


Last Updated: 20/07/2022 13:44:34
The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website