The days when mums found out they were having twins in the delivery suite are thankfully long gone! Chances are you’ll discover if you’re having twins at your first routine ultrasound scan. Usually this takes place between 10-14 weeks but you may have a scan earlier if you had fertility treatment, you’re not sure when your last period was, or if you’ve had symptoms such as bleeding. Early scans can occasionally miss twins, so you may not find out until your twins are spotted at a later scan.


As well as identifying the fact you have two babies, the first scan will tell you:

  • If the twins share an amniotic sac (monoamniotic twins) or have one each (diamniotic twins).
  • If the twins share a placenta (monochorionic twins) or have one each (dichorionic twins).

What to do when your scan shows you’re having twins

It can come as a huge shock to find out you’re carrying twins, and the sonographer may not be able to answer many of the questions that race through your mind. It’s a good time to contact an organisation such as Tamba (Twins And Multiple Births Association) or MBF (Multiple Births Foundation).

It’s worth asking your doctor at your early appointments what scans and tests you can expect and when. There’s a greater risk of complications when expecting twins, so you’ll need to visit the antenatal clinic more often and have more frequent scans. It’s likely you’ll still be given a local midwife or midwife team, but you may find more of your appointments are at hospital.

Although most women have no problems at all carrying twins, it’s worth being aware that there’s a higher risk of:

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  • Vaginal bleeding
  • Poor growth
  • Pre-eclampsia
  • Hydramnios (excess amniotic fluid)
  • Twin-to-twin transfusion syndrome (see below)
  • Premature labour

Screening tests

You’ll be offered various screening tests during your pregnancy to predict the likelihood of complications.

The test for Down’s syndrome is the nuchal translucency test, around 11-14 weeks, and sometimes a blood test.

If this shows a high risk of Down’s syndrome, you’ll be given the option of a further amniocentesis or Chorionic Villus Sampling (CVS) test on each baby. These are invasive tests, which involve taking amniotic fluid or tissue from the placenta, so you may be called to a specialist hospital. You should be given advice on the risks to your twins, to help you make your decision to test or not. As well as considering what the results of the test will mean to you, it’s particularly important to consider what you would do if only one twin was affected.

You may be offered a blood test called AFP (meaning alphfetoprotein) around 16 weeks to screen for spina bifida and other neural tube defects.

Tests for other genetic conditions, such as cystic fibrosis, may also be offered depending on your family history.

Anomaly ultrasound scan

Twin pregnancies will have the routine 20-22 week anomaly scan, which looks for any abnormalities, as a single pregnancy would. The sonographer will look closely at the spine, nervous system, abdominal wall and major organs. With twins, this will take twice as long, as there are two babies to check. It’s at this scan that the babies’ genders can often be identified, if you wish to know

More pregnancy ultrasound scans

Ultrasound scans are useful in a multiple pregnancy because other ways of monitoring healthy growth, such as measuring your bump, aren’t as accurate with twins as they are in a single pregnancy. Scans also monitor health and position and can pick up abnormalities, identify high-risk pregnancies or complications and check the twins’ interaction.

The number of scans you have overall will depend on how your babies are growing, as well as what type of twin pregnancy you have. It may also vary slightly from one hospital to another.

Dichorionic twins are lower risk so as a rough guide, you’ll have a scan at:

  • 20 weeks
  • 24 weeks
  • 28 weeks
  • 32 weeks
  • Then every fortnight until birth

These extra scans in late pregnancy are because twins’ growth may slow in the later weeks (compared to a single pregnancy), so they need to be closely monitored.


Monochorionic twins share a placenta, so there’s a risk of twin-to-twin transfusion syndrome. This is where one twin has a greater blood supply than the other. Women carrying monochorionic twins may be scanned as often as every fortnight after 16 weeks of pregnancy.