Surprised to discover you're expecting more than one child? Read on to find out what you should know about multiple pregnancies and what you should expect from your first visit to the hospital.

Finding out you are carrying twins (or more!) often comes as a great surprise to mothers-to-be. Few expectant mums anticipate that instead of carrying a child, they are carrying two, or in some cases, more! The concept of twins strikes many people as being mysterious and strange, when in reality, having twins is determined by straightforward, biological reasons.

How Did That Happen?
One in eighty pregnant women carry twins and one in 6400 carry triplets or more. Although multiple births are a rare occurrence, they are now more common than ever before due in part to the growing use of infertility treatments.

Peas in a pod
One third of twins born are identical. Identical twins are the same sex and look almost completely alike as they share the same genetic makeup. Identical twins are produced when a single egg that has been fertilised by a single sperm splits into two. Non-identical twins result from two eggs being fertilised by separate sperms. These twins are as similar or different as any other siblings would be. If you are carrying triplets, quads or more, they could be identical, non identical, or a mixture of both.

What are the chances?
Many factors can affect the likelihood of you carrying twins. Ethnicity is thought to be one, with people of African descent rated as the most likely ethnic group to carry twins, and Asians the least likely. From 35 years old, your chances of conceiving identical twins appears to rise, while paradoxically, your chances of conceiving non-identical twins falls. Some studies suggest that larger, taller women are 25-30% more likely to have twins and if twins are on your mother's side of the family, you are more likely to have a multiple pregnancy.

• Multiple births: Practical and financial benefits
  
• Soapbox: Multiple mums say 'Give us a break!'