This information is for general guidance only.

It does not replace advice from your midwife, obstetrician or fetal medicine team. Read more about our approach.

Twin pregnancy: everything you need to know

Expecting twins needs a bit more monitoring and care, but the vast majority of twin pregnancies result in two healthy babies. This guide covers how twins are classified, the extra care you will receive, and a quick tool to calculate your twin due date. Twin pregnancies carry a higher risk of pre-eclampsia in twin pregnancies and premature birth in twin pregnancies, both of which we cover in detail.

Twin due date calculator

Twin pregnancies are planned for earlier delivery than singletons to reduce the risk of stillbirth.

How common is a twin pregnancy?

Around 1 in 65 births in the UK involves twins. The rate has risen over the past few decades, partly because of IVF treatment and people having babies later in life.

How twins are formed

Identical (monozygotic) twins

  • One egg fertilised by one sperm, then splits into two embryos
  • Share exactly the same DNA
  • Always the same sex
  • May share a placenta (monochorionic) or have separate placentas
  • About one third of all twins

Non-identical (dizygotic) twins

  • Two separate eggs fertilised by two separate sperm at the same time
  • No more genetically alike than any other siblings
  • Can be the same sex or different sexes
  • Each baby has their own placenta (dichorionic)
  • More likely if twins run on the mother's side of the family, after 35, or following fertility treatment
  • About two thirds of all twins

Types of twins (by placenta)

The most important medical distinction is by placenta type (chorionicity). This determines how much monitoring is needed and when your twins will be delivered.

DCDA — Dichorionic Diamniotic

2 placentas, 2 sacs

  • All non-identical twins are DCDA.
  • Some identical twins are DCDA too.
  • The lowest-risk category for twin pregnancy.
  • Growth scans every 4 weeks from 16 weeks.
  • Planned delivery: 37 weeks.
MCDA — Monochorionic Diamniotic

1 shared placenta, 2 sacs

  • Most identical twins are MCDA.
  • Higher risk due to the shared placenta.
  • Risk of twin-to-twin transfusion syndrome (TTTS).
  • Scans every 2 weeks from 16 weeks.
  • Usually referred to a specialist fetal medicine unit.
  • Planned delivery: 36 weeks.
MCMA — Monochorionic Monoamniotic

1 shared placenta, 1 sac

  • The rarest type, under 1% of twin pregnancies.
  • Highest risk because of cord entanglement.
  • Intensive monitoring required.
  • Often managed with hospitalisation in the third trimester.
  • Always managed at a specialist centre.
  • Planned delivery: 32-33 weeks.

How twins are detected

Twins are usually discovered at your 12-week dating scan. Occasionally a woman feels larger than expected or has more severe morning sickness, which prompts an earlier scan.

The sonographer will determine

  • How many babies
  • How many placentas — chorionicity, which is crucial to establish before 14 weeks when it becomes harder to determine accurately

If chorionicity is unclear at your 11 to 14 week scan, a repeat scan will be offered within a few weeks to clarify.

Symptoms of a twin pregnancy

These are common in twin pregnancies, although none of them are definitive on their own.

  • More severe morning sickness (higher hCG levels)
  • A larger bump earlier than a singleton pregnancy
  • More fatigue, because your body is supporting two babies
  • More pronounced breast tenderness
  • Earlier fetal movements, as there is less space
  • Higher weight gain (typically 11-16kg for a healthy starting weight)

Antenatal care for twin pregnancies

Twin pregnancies receive more frequent antenatal care than singletons. Your team will include a consultant obstetrician alongside your community midwife.

DCDA scan schedule

  • 11-14 weeks: dating scan, confirm chorionicity
  • 20 weeks: anomaly scan
  • Every 4 weeks from 16 to 28 weeks: growth scans
  • Every 2 weeks from 28 weeks until delivery

MCDA scan schedule

  • 11-14 weeks: dating scan at specialist unit
  • 16-20 weeks: cervical length scan offered
  • Every 2 weeks from 16 weeks: detailed scans for TTTS
  • Any concerning signs trigger urgent specialist review

Additional monitoring for all twin pregnancies

  • More frequent blood pressure and urine checks (higher pre-eclampsia risk)
  • Additional blood tests for anaemia (more common with twins)
  • Consultant-led care rather than midwife-only

Twin-to-twin transfusion syndrome (TTTS)

TTTS only affects monochorionic twins (those sharing a placenta). It is caused by an imbalance of blood flow between the twins through abnormal vessel connections in the shared placenta. It affects 10 to 15% of MCDA twins.

One twin (the donor) becomes smaller and produces less urine. The other (the recipient) becomes larger and is at risk of heart problems from too much blood volume. TTTS is staged 1 to 5 (Quintero staging), with stage 5 the most severe.

Treatment is laser surgery to seal the connecting vessels, performed at specialist fetal medicine centres. Early detection through regular scanning is what makes treatment possible, which is why MCDA twins are scanned every 2 weeks.

Risks in twin pregnancies

Twin pregnancies carry higher risks than singletons. These are well managed with the right care.

  • Pre-term birth: most twins are born before 37 weeks, and around 6 in 10 twin pairs are born prematurely
  • Pre-eclampsia: significantly higher risk
  • Anaemia: more common due to increased blood volume demands
  • Gestational diabetes: higher risk
  • Placenta praevia: more common
  • Postpartum haemorrhage: higher risk because of a larger uterus
  • Babies at higher risk of low birth weight, neonatal unit care, and jaundice

Reassurance: the increased monitoring for twin pregnancies exists specifically to detect and manage these risks early. The majority of twin pregnancies result in two healthy babies.

Birth options for twins

Vaginal twin birth

  • Usually happens in a consultant-led hospital unit
  • Continuous monitoring of both babies in labour
  • An obstetric team is present throughout
  • After the first twin is born, the position of the second is assessed
  • Occasionally a caesarean is needed for the second twin

Caesarean for twins

  • Recommended if the first twin is not head-down
  • Planned at 36-37 weeks for DCDA, earlier for MCDA and MCMA
  • More common for twins than for singleton pregnancies

Read our c-section recovery guide for what to expect afterwards.

Preparing for twins

  • Consider a specialist twin pram rather than two separate prams.
  • A baby carrier (one twin at a time) is invaluable.
  • Accept every offer of help in the early weeks.
  • Twins Trust (twinstrust.org, 0800 138 0509) is the UK charity for multiple-birth families, offering practical support, courses and a helpline.
  • Twins Trust antenatal courses cover twin-specific preparation that standard antenatal classes may not include.

Related guides and tools

Pre-eclampsia guide→ Premature birth guide→ Breech baby (twin presentations)→ DVT risk with twins→

A note from our team

This guide reflects NHS UK, NICE and Twins Trust guidance. Your consultant and fetal medicine team are the best source of personalised advice for your twin pregnancy. Read more about us.

Frequently asked questions

How do I know if I am having twins?
Twins are usually detected at the 12-week dating scan. Some women suspect twins earlier because of more severe morning sickness, a larger bump for their dates, or a family history of twins. A simple ultrasound confirms how many babies there are and how many placentas, which is important for planning your care.
What is the difference between identical and non-identical twins?
Identical (monozygotic) twins come from one egg fertilised by one sperm that then splits into two embryos. They share the same DNA and are always the same sex. Non-identical (dizygotic) twins come from two separate eggs fertilised by two separate sperm at the same time, so they are no more alike than any other siblings and can be different sexes.
What is TTTS?
Twin-to-twin transfusion syndrome (TTTS) is a condition that can affect twins who share a placenta (monochorionic twins). Abnormal vessel connections cause an imbalance of blood flow between the twins: one becomes smaller and produces less urine, the other becomes larger and is at risk of heart strain. TTTS affects 10 to 15% of MCDA twins. It is treatable with laser surgery at specialist fetal medicine centres when detected early, which is why regular scans are so important.
When will I be delivered if I am having twins?
It depends on the type of twins. DCDA twins (separate placentas) are typically planned for 37 weeks. MCDA twins (shared placenta, separate sacs) for 36 weeks. MCMA twins (shared placenta and sac) around 32 to 33 weeks. Your consultant will confirm your individual plan based on how your pregnancy is progressing.
Can I have a natural birth with twins?
Most twin pregnancies can be born vaginally if the first baby is head-down and there are no other complications. Labour usually happens in a consultant-led hospital unit with continuous monitoring and an obstetric team present. A caesarean is more common with twins than singletons, and is recommended if the first twin is not head-down or for most MCDA and MCMA twins.
Will I see a consultant as well as a midwife?
Yes. Twin pregnancies are managed with consultant-led care alongside your community midwife. You will have more appointments and scans than a singleton pregnancy, and you will meet a consultant obstetrician regularly. MCDA and MCMA twins are usually referred to a specialist fetal medicine unit.