Having an ultrasound in the first trimester of pregnancy can be a thrilling experience. Bear in mind that you may need a second ultrasound before you know for certain if all is well.
It's wonderful to see a little blob with a heartbeat that will become your baby. If you are unsure of the first day of your last period you will be offered a dating ultrasound when you are between 10 and 14 weeks pregnant.
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.
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.
Instead, you will be offered a nuchal translucency ultrasound.
You should still have a ultrasound between 18 and 22 weeks because more detail can be seen as your baby grows bigger.
The dating ultrasound will also show if you're expecting twins, triplets or more.
It's helpful to know about twins early on, as it's easier to see whether or not they share a placenta.
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.
The LMP is used because most women know when their last period was, but may not know when they actually conceived.
If you do know the conception date, this is classed as day 14 and not day one.