When you're expecting twins or triplets, it's important that you attend all your appointments because of the increased risks with this type of pregnancy.
Your antenatal team should be experienced in caring for women having twins or triplets.
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 at around 11 to 14 weeks. 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.
You'll also be offered a scan, called an anomaly scan, around 18 to 20 weeks 6 days to check that your babies are developing normally.
Different types of twins
For medical purposes, there are 3 types of twins. These apply to triplets too, although a triplet pregnancy will be more complex than a twin one.
The 3 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 2 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 in 100 identical twins are MCMA.
The percentages of identical and non-identical twins born in the UK are not routinely recorded, but according to the Multiple Births Foundation about a 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.
If your babies are DCDA, the risks to their health in the womb are much lower. You'll usually be scanned every 4 weeks.
It's important to attend all your appointments so any problems can be picked up early and treated if necessary.
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're pregnant with 2 or more babies.
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 birthweight of under 2.5kg (5.5lb).
Most twins and triplets are born prematurely.
Around 6 in 10 twins are born before 37 weeks. Almost 8 in 10 triplets are born before 35 weeks.
If you are expecting twins or triplets, you will be offered a planned birth at:
- 37 weeks for twins with a placenta each
- 36 weeks for identical twins sharing a placenta
- 35 weeks for an uncomplicated triplet pregnancy
- 32-33 weeks for MCMA twins
It can be dangerous for twin and triplet pregnancies to carry on after the planned birth dates. Plans for the birth will be discussed with you taking into account your needs and preferences.
If you turn down the offer of a planned birth, you will be offered weekly appointments with an obsetrician and weekly ultrasound scans plus a foetal growth scan every 2 weeks.
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
Twin-twin transfusion syndrome (TTTS) affects identical twins who share a placenta (monochorionic).
The risk is higher for MCDA twins, but it can happen in MCMA twins, too.
It's caused by abnormal connecting blood vessels in the twins' placenta.
This results in an imbalanced blood flow from 1 twin (known as the donor) to the other (recipient), leaving 1 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 a doctor, as what works in one TTTS pregnancy may not be appropriate in another.