It will usually take place at your local hospital ultrasound department.The person performing the scan is called a sonographer.The screening test for Down's syndrome used at this stage of pregnancy is called the "combined test".It involves a blood test and measuring the fluid at the back of the baby's neck (nuchal translucency) with an ultrasound scan.
Finding out about having twins early in pregnancy also gives you more time to prepare for the birth and for your doctor or midwife to plan your care.
Knowing about twins early is also useful if you want to have screening for Down's syndrome.
This is because blood tests for Down's syndrome are not very accurate if you are having more than one baby.
But ultrasounds can also lift the lid on a few worries you might be having. The main reason for the ultrasound is to work out how many weeks pregnant you are, and to estimate your due date.
The length of your pregnancy is calculated from the first day of your last menstrual period (LMP), even though you don't actually conceive until 14 days after your LMP, and later than this if your cycle is longer than 28 days.