Surprise twins have are a mainstay of film and fiction, but in the modern world it seems impossible that anyone wouldn’t be aware that they’re carrying an extra baby. It is true that hidden twins are very rare in countries like the UK where women have access to ultrasound scans and high quality maternity care. However, there is a very small chance that a twin can be missed on a scan, particularly during early pregnancy. twins ultrasound scan Finding Out You’re Expecting Twins In most cases, if you’re expecting twins or more then you will find out as soon as you have your first ultrasound scan. The sonographer or doctor will quickly see that there is more than one baby. In many cases there will be multiple amniotic sacs too, although identical twins may be sharing one. You will usually be able to listen to each baby’s heartbeat and to take a close look at them on the screen while they are being measured and examined. Hidden Twins However, there are a very small number of cases in which a twin is not spotted right away. It is very unlikely that this would happen on a later ultrasound, but if you are having an early pregnancy scan within the first trimester it is possible, though incredibly rare. The baby’s heartbeat can’t usually be detected before about 7-8 weeks, but some scans are performed before this. If one of the tiny twins happens to be hidden behind the other when the scan is performed, then there might not be any clue that you’re carrying more than one baby. You might only find out that the second baby is there when you have another scan later in the pregnancy. If you are expecting more than one baby then you should talk to your midwife or obstetrician about how a multiple pregnancy and birth will affect you and your babies. You should also expect to have longer ultrasound appointments in the future as both babies will need to be checked in turn.